Definition: In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.
Input: Passage: The military history of the Aleutian Islands began almost immediately following the purchase of Alaska from the Russian Empire by the United States in 1867. Prior to the early 20th century, the Aleutian Islands were essentially ignored by the United States Armed Forces, although the islands played a small role in the Bering Sea Arbitration when a number of British and American vessels were stationed at Unalaska to enforce the arbitrators' decision. By the early 20th century, a number of war strategies examined the possibility of conflict breaking out between the Empire of Japan and the United States. While the Aleutian Islands were seen as a potential staging point for invasions by either side, this possibility was dismissed owing to the islands' dismal climate. In 1922, the Washington Naval Treaty was signed, after which the United States Navy began to take an interest in the islands. However, nothing of significance was to materialize until World War II.
Link Information: the Imperial Japanese Navy at the same time made its surprise attack on Pearl Harbor in Honolulu on December 7, 1941 Answer: December 7, 1941
Output:
When did the empire that could potentially invade the islands first experience military conflict with the United States?