Japanese-American Claims Act
The attack on Pearl Harbor was a surprise military strike by the Imperial Japanese Navy on the United States naval base at Pearl Harbor in Honolulu, Hawaii, on the morning of December 7, 1941. The attack sank four U.S. battleships, destroyed 188 U.S. aircraft, and killed 2,403 U.S. citizens within two hours, and led to the United States joining World War II. Once the United States entered the war and anti-Japanese sentiment began to circulate, Americans increasingly reacted with racism and hostility, viewing people of Japanese descent were treated as enemies regardless of whether they were U.S. citizens. The U.S. government expressed concerns about the loyalty of the Japanese people living in America and about Japanese spies sending information to Japan. "The U.S. Department of the Treasury froze the assets of all citizens and resident aliens who were born in Japan, and the Department of Justice arrested some 1,500 religious and community leaders as potentially dangerous enemy aliens. Because many of the largest populations of Japanese Americans were in close proximity to vital war assets along the Pacific coast. The result was President Franklin D. Roosevelt's Executive Order 9066."
Nuclear warfare
In late June 1945, as the U.S. wrapped up the two-and-a-half-month Battle of Okinawa (which cost the lives of 260,000 people, including 150,000 civilians), it was faced with the prospect of invading the Japanese home islands in an operation codenamed Operation Downfall. Based on the U.S. casualties from the preceding island-hopping campaigns, American commanders estimated that between 50,000 and 500,000 U.S. troops would die and at least 600,000–1,000,000 others would be injured while invading the Japanese home islands. The U.S. manufacture of 500,000 Purple Hearts from the anticipated high level of casualties during the U.S. invasion of Japan gave a demonstration of how deadly and costly it would be. President Harry S. Truman realized he could not afford such a horrendous casualty rate, especially since over 400,000 American combatants had already died fighting in both the European and the Pacific theaters of the war.