As an expert in historical studies, I can provide a comprehensive analysis of the factors leading to the United States' entry into World War II. It is important to note that the decision to enter the war was not a result of a single event, but rather a culmination of various factors and events that unfolded over time.

Step 1: The Context of the 1930s
The 1930s were marked by the Great Depression, which had a profound impact on the United States and its global outlook. The economic crisis led to a focus on domestic recovery, encapsulated by President Franklin D. Roosevelt's New Deal policies. This inward focus, coupled with a strong sense of isolationism prevalent among the American public, meant that the U.S. was initially reluctant to involve itself in the escalating conflicts in Europe and Asia.

Step 2: The Rise of Aggressive Powers
The rise of totalitarian regimes in Germany, Italy, and Japan, each with expansionist ambitions, was a significant factor. Nazi Germany, under Adolf Hitler, began to rearm and expand its military in defiance of the Treaty of Versailles. This, along with Italy's invasion of Ethiopia and Japan's aggressive moves in China and Southeast Asia, signaled a growing threat to global peace.

Step 3: The Failure of Appeasement
The policy of appeasement, particularly by Britain and France, aimed to satisfy the territorial demands of the aggressive powers to avoid war. However, this policy failed to contain the ambitions of Hitler, Mussolini, and the Japanese militarists, and instead, it emboldened them.

**Step 4: The Fall of France and the Battle of Britain**
The fall of France to Germany in 1940 and the subsequent Battle of Britain marked a turning point. The U.S. began to provide aid to the United Kingdom through the Lend-Lease program, which allowed Britain to receive military supplies without immediate payment. This was a significant step away from neutrality.

**Step 5: The Japanese Expansion and the Tripartite Pact**
Japan's continued expansion in the Pacific, including the occupation of French Indochina, and the signing of the Tripartite Pact by Germany, Italy, and Japan in 1940, which formed an Axis alliance, heightened tensions with the U.S.

**Step 6: Economic Sanctions and Diplomatic Breakdown**
In response to Japan's aggressive actions, the U.S. imposed economic sanctions, including an embargo on oil and other critical materials. Diplomatic relations deteriorated, and negotiations between the two nations failed to produce a peaceful resolution.

Step 7: The Attack on Pearl Harbor
The redacted event that directly led to the U.S. entry into World War II was the surprise military strike by the Japanese Navy Air Service against the U.S. naval base at Pearl Harbor, Hawaii, on December 7, 1941. The attack severely damaged the U.S. Pacific Fleet and resulted in the deaths of over 2,400 Americans. The next day, President Roosevelt delivered his famous "Infamy Speech" to Congress, and the U.S. formally declared war on Japan.

**Step 8: Declaration of War and Entry into Global Conflict**
Following the attack on Pearl Harbor, the United States declared war on Japan, and within days, Germany and Italy declared war on the U.S., bringing the country fully into the global conflict.

**Step 9: The Impact on the American Homefront**
The entry into the war marked a significant shift in the American homefront, with a massive mobilization of industry, resources, and citizens towards the war effort. It also led to the internment of Japanese Americans, which is now widely recognized as a grave injustice.

Step 10: The Long-term Consequences
The U.S. involvement in World War II had profound and lasting effects on the country and the world. It marked the beginning of the U.S. as a superpower and set the stage for the Cold War and the post-war international order.

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Although the war began with Nazi Germany's attack on Poland in September 1939, the United States did not enter the war until after the Japanese bombed the American fleet in Pearl Harbor, Hawaii, on December 7, 1941.read more >>