Periodically, tensions flare up between Japan and China over a small group of Japanese-administered islands located in the East China Sea. Japan, China, and Taiwan all claim sovereignty over the islands, known as the Senkaku-shoto in Japan, the Diaoyu Dao in China, and the Diaoyutai Lieyu in Taiwan. The land features in question are eight in number, sometimes described as five islands and three rocks, and are uninhabited. The largest, Uotsurijima (Diaoyudao/Diaoyutai), is roughly 1.5 square miles (941 acres) in area, a bit larger than New York City's Central Park. The others range in size from the Tobise (Fei Yu/Feilai) rock cluster's half an acre to Kubajima's (Huangwei Yu/ Huangwei Islet) 0.35 square miles (224 acres). Some geologists believe that the waters surrounding them may be rich in oil and natural gas deposits. Although it has become conventional to refer to the Senkakus as "islands," some observers might argue that they may not qualify legally as islands for purposes of generating maritime zone entitlements under the United Nations Convention on the Law of the Sea (UNCLOS). The gravity of the dispute between Japan and China over the Senkakus (Diaoyu/Diaoyutai) has increased since 2010, featuring episodic eruptions of crises between the two countries. Events in 2012 dramatically intensified matters. In September of that year, Japan's central government purchased three of the islands from their private owner in order to preempt a Japanese nationalist who had raised nearly $20 million to purchase the islands. China and Taiwan protested the move, and across China large-scale anti-Japanese protests erupted, some of which resulted in violence. Additionally, since the Japanese government nationalized the three islands, China has markedly increased its deployments of maritime law enforcement and naval ships near the islands and increased military patrol flights in the East China Sea, prompting reciprocal responses from the Japanese Coast Guard and Japanese Air Self Defense Force (Japan's Air Force). The frequent proximity of the two countries' ships and planes to one another has prompted worries from many about a collision or skirmish, which could draw in the United States due to its treaty commitment to help protect Japan and the specific U.S. interpretation that its treaty commitment applies to the disputed territory. Each time a crisis has erupted over the Senkakus (Diaoyu/Diaoyutai), questions have arisen concerning the U.S. relationship to the islands. This report focuses on that issue, which has four elements: 1. U.S. administration of the islands from 1953 to 1971, when the United States occupied Okinawa; 2. the application to the Senkakus (Diaoyu/Diaoyutai) of the 1971 "Treaty Between Japan and the United States of America Concerning the Ryukyu Islands and the Daito Islands"—commonly known as the Okinawa Reversion Treaty, which was approved by the Senate in 1971 and entered into force the following year (the Daito Islands lie to the east of Okinawa); 3. the U.S. view on the claims of the disputants; and 4. the relationship of the 1960 U.S.-Japan Security Treaty to the islands. For additional information and analysis on the geopolitical aspects of this and other maritime disputes, see CRS Report R42784, China's Actions in South and East China Seas: Implications for U.S. Interests—Background and Issues for Congress , by Ronald O'Rourke; CRS Report R42930, Maritime Territorial Disputes in East Asia: Issues for Congress , by Ben Dolven, Mark E. Manyin, and Shirley A. Kan; and CRS Report RL33740, The U.S.-Japan Alliance , by Emma Chanlett-Avery and Ian E. Rinehart. The claims of China and Taiwan to sovereignty over the Senkakus (Diaoyu/Diaoyutai) have a similar basis. China asserts that its Ming Dynasty (1368-1644) considered the islands part of its maritime territory and included them on maps and documents of areas covered by Ming Dynasty coastal defenses. According to China, the Qing Dynasty (1644-1911) went further and placed them under the jurisdiction of Taiwan, which was a part of the Qing Dynasty. However, although there are claims that Chinese fishermen used the islands as places of temporary shelter and repair, China does not appear to have ever established a permanent settlement of civilians or military personnel, and apparently did not maintain permanent naval forces in adjacent waters. Japan, which rejects the existence of a territorial dispute, laid claim to the Senkakus (Diaoyu/Diaoyutai) on January 14, 1895, when the Japanese Cabinet issued a decision to formally incorporate them into Japanese territory. Before then, Japan argues, the islands were uninhabited, without owner ( terra nullius) , and "showed no trace of having been under the control of China." The Chinese and Taiwanese governments reject Japan's terra nullius claim. For several years after Japan claimed the territory, a Japanese citizen, Tatsuhiro Koga, established settlements on some of the islands to extract materials—including bonito and guano—from the land and the surrounding waters. In May 1895, Japan and the Qing Dynasty government of China signed the Treaty of Shimonoseki ending the Sino-Japanese war that had begun the previous year. Under the pact, which China today considers one of a number of "unequal treaties" forced on it by foreign powers, China ceded Taiwan (Formosa) to Japan "together with all the islands appertaining or belonging to the said island of Formosa." The Treaty did not specifically mention the Senkakus (Diaoyu/Diaoyutai) and the islands were not discussed during the negotiating sessions. Japan has claimed from this that its incorporation of the Senkakus (Diaoyu/Diaoyutai) was an act apart from the Sino-Japanese War. In contrast, China and Taiwan argue that Japan used its victory in the war to annex the Senkakus (Diaoyu/Diaoyutai). As an extension of this argument that Japan took the islands by force from China, Beijing and Taipei also argue that the Allied declarations at Cairo and Potsdam during World War II—which vowed to restore to China territories taken from it by Japan through military aggression—apply to the Senkakus (Diaoyu/Diaoyutai), which therefore should have been returned to China. In October 1945, when Japan relinquished authority over Taiwan, it did not specifically mention the disposition of the islands. U.S. administration of the islands began after World War II, as a result of the 1951 Treaty of Peace with Japan. The Treaty did not mention the Senkakus (Diaoyu/Diaoyutai), but it referred to other locations that had reverted to Chinese control or which China claimed. These included Taiwan and the Pescadores (off the western coast of Taiwan), as well as the Spratlys and the Paracels (both in the South China Sea). Article 3 gave the United States sole powers of administration of "Nansei Shoto south of 29 north latitude (including the Ryukyu and the Daito Islands)…." In 1953, the U.S. Civil Administration of the Ryukyus issued U.S. Civil Administration of the Ryukyus Proclamation 27 (USCAR 27), which defined the boundaries of "Nansei Shoto [the southwestern islands] south of 29 degrees north latitude" to include the Senkakus (Diaoyu/Diaoyutai islands). At the time of the signing of the Okinawa Reversion Treaty in 1971, several State Department officials asserted that following the signing of the Japan Peace Treaty, "Nansei Shoto south of 29 degrees north latitude" was "understood by the United States and Japan to include the Senkaku Islands." Moreover, during the period of U.S. administration, the U.S. Navy established firing ranges on some of the islands and paid an annual rent of $11,000 to Jinji Koga, son of Tatsushiro Koga who had created extractive settlements on some of the islands. China has described the U.S.-Japan understandings related to the islands as "backroom deals" that are "illegal and invalid." The Okinawa Reversion Treaty, which was signed on June 17, 1971, and entered into force on May 15, 1972, provided for the return to Japan of "all and any powers of administration, legislation and jurisdiction" over the Ryukyu and Daito islands, which the United States had held under the Japan Peace Treaty. Article I of the Okinawa Reversion Treaty defines the term "the Ryukyu Islands and the Daito Islands" as "all territories with their territorial waters with respect to which the right to exercise all and any powers of administration, legislation and jurisdiction was accorded to the United States of America under Article 3 of the Treaty of Peace with Japan.... " An Agreed Minute to the Okinawa Reversion Treaty defines the boundaries of the Ryukyu Islands and the Daito islands "as designated under" USCAR 27. Moreover, the latitude and longitude boundaries set forth in the Agreed Minute appear to include the Senkakus (Diaoyu/Diaoyutai). A letter of October 20, 1971, by Robert Starr, Acting Assistant Legal Adviser for East Asian and Pacific Affairs—acting on the instructions of Secretary of State William Rogers—states that the Okinawa Reversion Treaty contained "the terms and conditions for the reversion of the Ryukyu Islands, including the Senkakus." During Senate deliberations on whether to consent to ratification of the Okinawa Reversion Treaty, the State Department asserted that the United States took a neutral position with regard to the competing claims of Japan, China, and Taiwan, despite the return of the Senkakus (Diaoyu/Diaoyutai) to Japanese administration. State Department officials asserted that reversion of administrative rights to Japan did not prejudice any sovereignty claims. When asked by the then-chairman of the Senate Foreign Relations Committee how the Okinawa Reversion Treaty would affect the determination of sovereignty over the Senkakus (Diaoyu/Diaoyutai), Secretary of State William Rogers answered that "this treaty does not affect the legal status of those islands at all." In his letter of October 20, 1971, Acting Assistant Legal Adviser Robert Starr stated: The Governments of the Republic of China and Japan are in disagreement as to sovereignty over the Senkaku Islands. You should know as well that the People's Republic of China has also claimed sovereignty over the islands. The United States believes that a return of administrative rights over those islands to Japan, from which the rights were received, can in no way prejudice any underlying claims. The United States cannot add to the legal rights Japan possessed before it transferred administration of the islands to us, nor can the United States, by giving back what it received, diminish the rights of other claimants. The United States has made no claim to the Senkaku Islands and considers that any conflicting claims to the islands are a matter for resolution by the parties concerned. Successive U.S. Administrations have restated this position of neutrality regarding the sovereignty claims, particularly during periods when tensions have flared, as in 1996, 2010, and 2012. In providing its consent to U.S. ratification of the Treaty, the Senate did not act on the advice of committee witnesses who objected to the inclusion of the Senkakus (Diaoyu/Diaoyutai) in the reversion of Okinawa and surrounding territories to Japan. Article 5 of the 1960 U.S.-Japan Security Treaty stipulates that Each Party recognizes that an armed attack against either Party in the territories under the administration of Japan would be dangerous to its own peace and safety and declares that it would act to meet the common danger in accordance with its constitutional provisions and processes. [emphasis added] Thus, "administration" rather than "sovereignty" is the treaty's key distinction. The inclusion of the Senkakus (Diaoyu/Diaoyutai) in the Okinawa Reversion Treaty under the definition of "the Ryukyu Islands and the Daito Islands" made the Security Treaty applicable to the islands. Further cementing the linkage, Article II of the Okinawa Reversion Treaty states that "treaties, conventions and other agreements concluded between Japan and the United States of America, including, but without limitation to the Treaty of Mutual Cooperation and Security between Japan and the United States of America ... become applicable to the Ryukyu Islands and the Daito Islands as of the date of entry into force of this Agreement." Using "Okinawa" as shorthand for the territory covered by the Treaty, then-Secretary of State Rogers stated in his testimony before the Senate Foreign Relations Committee that the 1960 U.S.-Japan Security Treaty "becomes applicable to Okinawa" in the same way as it applied to the Japanese home islands. Then-Deputy Secretary of Defense David Packard, in his testimony, stressed that Japan would assume the "primary responsibility" for the defense of the treaty area but that the Security Treaty was applicable. In short, while maintaining neutrality on the competing claims, the United States agreed in the Okinawa Reversion Treaty to apply the Security Treaty to the treaty area, including the Senkakus (Diaoyu/Diaoyutai). During the 2010 worsening of Japan-PRC relations over the disputed territory, then-Secretary of State Clinton summed up the U.S. stance by stating, "... with respect to the Senkaku Islands, the United States has never taken a position on sovereignty, but we have made it very clear that the islands are part of our mutual treaty obligations, and the obligation to defend Japan." In 2012, China began regularly deploying maritime law enforcement ships near the Senkakus (Diaoyu/Diaoyutai) and stepped up what it called "routine" patrols to assert jurisdiction in "China's territorial waters." China was responding to the Japanese central government's September 2012 purchase of three of the islands from their private owner. Since then, China has maintained and occasionally increased these patrols around the islands, perhaps to test Japan's resolve, and has increased military patrol flights in the East China Sea, prompting reciprocal responses from the Japanese Coast Guard and the Japanese Air Self Defense Force. China's increase in patrols around the Senkakus (Diaoyu/Diaoyutai) since the fall of 2012 appears to many to be an attempt to demonstrate that Beijing has a degree of administrative control over the disputed territory, thereby exploiting the U.S. distinction between sovereignty and administrative control. Thereafter, some observers, seeking to avoid a situation where the United States inadvertently encourages more assertive Chinese actions, called on Obama Administration officials to stop using the word "neutral" in describing the U.S. position on the issue and also to publicly declare that unilateral actions by China (or Taiwan) will not affect the U.S. judgment that the territory is controlled by Japan. In its own attempt to address this perceived gap, Congress inserted in the FY2013 National Defense Authorization Act ( H.R. 4310 , P.L. 112-239 ) a resolution stating, among other items, that "the unilateral action of a third party will not affect the United States' acknowledgment of the administration of Japan over the Senkaku Islands," language that since 2012 has reappeared in a number of bills and resolutions concerning U.S. interests in the East China Sea. In January 2013 then-Secretary Clinton stated that "we oppose any unilateral actions that would seek to undermine Japanese administration" of the islands during remarks to the press with the Japanese Foreign Minister. Speaking to the press with Prime Minister Shinzo Abe in Tokyo in April 2014, President Obama underscored the U.S. commitment in what are believed to be the first public remarks by a U.S. President stating the U.S. position on the Senkakus (Diaoyu/Diaoyutai) dispute. In his prepared remarks, the President said We stand together in calling for disputes in the region, including maritime issues, to be resolved peacefully through dialogue. We share a commitment to fundamental principles such as freedom of navigation and respect for international law. And let me reiterate that our treaty commitment to Japan's security is absolute, and Article 5 covers all territories under Japan's administration, including the Senkaku Islands .... [emphasis added] During the same press conference, President Obama responded to a questioner asking why he had chosen to speak about the Senkakus: Our position is not new. Secretary Hagel, our Defense Secretary, when he visited here, Secretary of State John Kerry when he visited here, both indicated what has been our consistent position throughout. We don't take a position on final sovereignty determinations with respect to Senkakus, but historically they have been administered by Japan and we do not believe that they should be subject to change unilaterally . And what is a consistent part of the alliance is that the treaty covers all territories administered by Japan. So this is not a new position, this is a consistent one. [emphasis added] In our discussions, I emphasized with Prime Minister Abe the importance of resolving this issue peacefully—not escalating the situation, keeping the rhetoric low, not taking provocative actions, and trying to determine how both Japan and China can work cooperatively together.... Speaking at a joint press conference with Japanese Defense Minister Tomomi Inada in Tokyo in February 2017 on his first overseas trip after becoming President Donald Trump's Secretary of Defense, Jim Mattis said "... I made clear that our longstanding policy on the Senkaku Islands stands. The United States will continue to recognize Japanese administration of the islands, and as such article five of the U.S.-Japan Security Treaty applies." Inada said that, in addition, during their meetings, Mattis said that "United States opposes any unilateral action to attempt to overthrow Japan's administration of the Senkaku Islands." In February 2017, during his first joint press appearance as President with Prime Minister Shinzo Abe, President Donald Trump stated that "we are committed to the security of Japan and all areas under its administrative control.... " A joint statement issued by the two governments during their summit said that the two leaders "affirmed that Article V of the U.S.-Japan Treaty of Mutual Cooperation and Security covers the Senkaku Islands. They oppose any unilateral action that seeks to undermine Japan's administration of these islands." In response, a Chinese Foreign Ministry spokesperson said "China is gravely concerned about and firmly opposed to relevant comments by Japan and the United States.... We are firmly against Japan's attempt to try to gain U.S. support for its illegal territorial claims in the name of the so-called mutual defense treaty. Japan and the U.S. should exercise prudence and stop making wrong remarks so as not to complicate relevant issues or bring negative impact on regional peace and stability." The expanded U.S. rhetorical support for Japan on the dispute has been accompanied by increasing bilateral diplomatic coordination on responding to China's increased assertiveness in the South China Sea, as well as increased bilateral security cooperation to boost Japan's maritime and island defenses. Since at least 2012, the United States has increased sales of advanced air and naval equipment to Japan, and the two countries in 2015 revised their bilateral defense guidelines, which provide a framework for alliance cooperation, in part to make the U.S.-Japan alliance better able to function in a contingency involving conflict between Japan and China in the East China Sea. As laid out in the U.S. Defense Department's 2015 Asia-Pacific Maritime Security Strategy, these moves are part of the overall U.S. policy of attempting to "deter conflict and coercion." 

Summary: Since the mid-1990s, and particularly since 2012, tensions have spiked between Japan and China over the disputed Senkaku (Diaoyu/Diaoyutai) islands in the East China Sea. These flare-ups run the risk of involving the United States in an armed conflict in the region. Japan administers the eight small, uninhabited features, the largest of which is roughly 1.5 square miles. Some geologists believe the features sit near significant oil and natural gas deposits. China, as well as Taiwan, contests Japanese claims of sovereignty over the islands, which Japan calls the Senkaku-shoto, China calls the Diaoyu Dao, and Taiwan calls the Diaoyutai Lieyu. Although the disputed territory commonly is referred to as "islands," it is unclear if any of the features would meet the definition of "island" under international law. U.S. Administrations going back at least to the Nixon Administration have stated that the United States takes no position on the question of who has sovereignty over the Senkakus (Diaoyu/Diaoyutai). It also has been U.S. policy since 1972, however, that the 1960 U.S.-Japan Security Treaty covers the islands. The treaty states that the United States is committed to "meet the common danger" of an armed attack on "the territories under the Administration of Japan," and Japan administers the Senkakus (Diaoyu/Diaoyutai). In return for U.S. security commitments, Japan grants the United States the right to station U.S. troops—which currently number around 50,000—at dozens of bases throughout the Japanese archipelago. Although it is commonly understood that Japan will assume the primary responsibility for the defense of the treaty area, in the event of a significant armed conflict with either China or Taiwan, most Japanese likely would expect that the United States would honor its treaty obligations. Since 2012, without challenging the U.S. government's position of neutrality over who has sovereignty over the islands, Congress nevertheless has expanded rhetorical support for Japan on the dispute. Congress inserted in the FY2013 National Defense Authorization Act (H.R. 4310/P.L. 112-239) a resolution stating, among other items, that "the unilateral action of a third party will not affect the United States' acknowledgment of the administration of Japan over the Senkaku Islands." Following Congress's statement, Obama Administration officials began using similar language, also without changing U.S. neutrality on the sovereignty question. Most prominently, in April 2014, President Obama reiterated that Article 5 of the U.S.-Japan Security Treaty covers the islands and that "we do not believe that [the Senkakus' status] ... should be subject to change unilaterally." This is believed to be the first time a U.S. President publicly stated the U.S. position on the dispute. In February 2017, during his first joint press appearance as President with Prime Minister Shinzo Abe, President Donald Trump stated that "we are committed to the security of Japan and all areas under its administrative control.... " A joint statement issued by the two governments during their summit said that the two leaders "affirmed that Article V of the U.S.-Japan Treaty of Mutual Cooperation and Security covers the Senkaku Islands. They oppose any unilateral action that seeks to undermine Japan's administration of these islands." The expanded U.S. rhetorical support for Japan has been a reaction to China's increasing patrols around the Senkakus (Diaoyu/Diaoyutai) beginning in the fall of 2012, moves that appear to many to be an attempt to exploit the U.S. distinction between sovereignty and administrative control by demonstrating that Beijing has a degree of administrative control over the islands. In a further effort to deter Chinese actions, the United States has increased its support for Japan's efforts to boost its maritime and island defenses. Each time tensions over the territorial dispute have flared, questions have arisen concerning the U.S. legal relationship to the islands. This report focuses on that issue.