第一次台湾海峡危機
紛争
アメリカ合衆国のハリー・S・トルーマン大統領は1950年1月5日に米国は台湾海峡に関するいかなる紛争にも関わることはなく中華人民共和国の攻撃があっても介入することはないとする「台湾不干渉声明」を発表した。しかし1950年6月25日に朝鮮戦争が勃発すると、トルーマンは「台湾海峡の中立化」はアメリカ合衆国にとって最大の関心事であると表明し、事実上アメリカの保護下に台湾を置きながら中華民国と中華人民共和国の紛争を防ぐ為に台湾海峡にアメリカ海軍の第7艦隊を派遣した。
1950年6月27日にトルーマン大統領は以下のコメントを発表した。
"韓国への攻撃は、共産主義者が主権国家を征服するために国家転覆の範疇を超え、今や武力による侵略と戦争を使用するであろうことを疑いなく明白にしている。 それは国際的な平和と安全を守るために発行された国連安全保障理事会の決議に違反しています。 このような状況では、共産軍による台湾の占領は、太平洋地域の安全保障と、その地域で合法的かつ必要な機能を実行する米軍にとって直接的な脅威となるでしょう。 したがって、私はアメリカ海軍第7艦隊に台湾への攻撃を防ぐよう命令した。この行動の結果として、私は台湾の中国国民政府に対して中国本土に対する航空と海上作戦をすべて中止するよう要請している。 台湾の将来の地位の決定は、太平洋における安全保障の回復、日本との和平の解決、または国連による検討を待たなければならない。"
President Truman later ordered John Foster Dulles, the Foreign Policy Advisor to U.S. Secretary of State Dean Acheson, to carry out his decision on neutralizing Taiwan in drafting the  Treaty of San Francisco of 1951 (the peace treaty with Japan), which excluded the participation of both the ROC and the PRC. No recipient was specified in the treaty of Taiwan's sovereignty, which supporters of Taiwan independence have used to argue for their position. According to the author George H. Kerr, a supporter of Taiwanese independence, in his book Formosa Betrayed, the political status of Taiwan was under the trust of the Allied Powers (against Japan). It would be the responsibility of the United Nations if this could not be resolved in near future as designed in the peace treaty.
The Nationalist Chinese Government maintained as its goal the recovery of control of mainland China, and this required a resumption of the military confrontation with the Red Chinese. Truman and his advisors regarded that goal as unrealizable, but regrets over losing China to international communism was quite prominent in public opinion at the time, and the Truman Administration was criticized by anticommunists for preventing any attempt by Chiang Kai-shek's forces to liberate mainland China.
Truman, a member of the Democratic Party did not run for reelection in the presidential election of 1952, even though he was eligible to do so. This election was won by the Republican Dwight Eisenhower, a World War II general.
On February 2, 1953, the new President lifted the Seventh Fleet's blockade in order to fulfill demands by anticommunists to "unleash Chiang Kai-shek" on mainland China.
In August 1954, the Nationalists placed 58,000 troops on Quemoy and 15,000 troops on Matsu. The ROC began building defensive structures and the PRC began shelling ROC installations on Quemoy.  Zhou Enlai, Premier of the People's Republic of China responded with a declaration on August 11, 1954, that Taiwan must be "liberated."  He dispatched the People's Liberation Army (PLA) to the area, and it began shelling both Quemoy and the Matsu Islands.
Despite warnings from the U.S. against any attacks on the Republic of China; five days before the signing of the Manila pact, the PLA unleashed a heavy artillery bombardment of Quemoy on September 3, and intensified its actions in November by bombing the Tachen Islands. This renewed Cold War fears of Communist expansion in Asia at a time when the PRC was not recognized by the United States Department of State. Chiang Kai Shek's government was supported by the United States because the ROC was part of the Containment of Communism which stretched from a devastated South Korea to an increasingly divided Southeast Asia.
On September 12, the U.S. Joint Chiefs of Staff recommended the use of nuclear weapons against mainland China. Eisenhower, however, resisted pressure to use nuclear weapons or involve American troops in the conflict. However, on December 2, 1954, the United States and the ROC agreed to the Sino-American Mutual Defense Treaty, which did not apply to islands along the Chinese mainland. This treaty was ratified by the U.S. Senate on February 9, 1955.
After two failed attempts, the PLA seized the Yijiangshan Islands on January 18, 1955. Fighting continued in nearby islands off the coast of Zhejiang, as well as around Quemoy and the Matsu Islands in Fujian. On January 29, 1955, the Formosa Resolution was approved by both houses of the U.S. Congress authorizing Eisenhower to use U.S. forces to defend the ROC and its possessions in the Taiwan Strait against armed attack.
In February, British Prime Minister Winston Churchill warned the U.S. against using nuclear weapons, but in March, U.S. Secretary of State John Foster Dulles stated publicly that the U.S. was seriously considering a nuclear strike. In response, the NATO foreign ministers warned at a meeting of the alliance against such action. In late March, U.S. Admiral Robert B. Carney said that Eisenhower is planning "to destroy Red China's military potential."
Aftermath
Some scholars have argued that the PRC backed down in the face of American nuclear brinksmanship and in light of the lack of willingness by the Soviet Union to threaten nuclear retaliation for an attack on the PRC. Others see the case as an example of effective application of extended deterrence by the United States. In any case, the Red Chinese government stated on April 23, 1955, that it was willing to negotiate. On May 1 the PLA temporarily ceased shelling Quemoy and Matsu. The fundamental issues of the conflict remained unresolved, however, and both sides subsequently built up their military forces on their respective sides of the Taiwan Strait leading to a new crisis three years later. There are strong indications that Mao used the crisis in order to provoke the United States into making nuclear threats. Other scholars have argued that Mao and the Soviet leadership carefully pursued a limited aims strategy to boost morale and for domestic political gain by seizing the Dachens and had no intention to escalate the conflict with the United States.