2. Unrestricted Submarine Warfare: Germany's resumption of unrestricted submarine warfare, targeting merchant ships without warning, posed a significant threat to U.S. commerce and shipping. This led to increased tensions and incidents between Germany and the United States.
3. German Aggression in Europe: The United States had growing concerns about Germany's aggressive actions in Europe, including the invasion and occupation of several countries. The U.S. feared that Germany's expansionism and military power could pose a direct threat to the United States and its interests.
4. Isolationist Sentiment: Although the United States initially adopted a policy of isolationism, public opinion gradually shifted towards supporting involvement in the war as news of the atrocities committed by the Axis powers became more widely known. The American public became more concerned about the humanitarian implications and the potential threat to democracy.
5. Lend-Lease Program: The United States had already been providing aid to the Allies through the Lend-Lease program, but the attack on Pearl Harbor accelerated this support. The provision of military equipment, supplies, and financial aid to the Allies, particularly Great Britain, increased the U.S. involvement in the war.
6. Diplomatic Failures and Ultimatums: Despite attempts at diplomacy and negotiations, Germany's unwillingness to compromise or halt its aggressive actions led to the failure of diplomatic efforts. Ultimatums issued by the United States, demanding an end to unrestricted submarine warfare and the withdrawal of German forces from occupied territories, were met with resistance.
7. Influence of Public Opinion: Public opinion in the United States played a significant role in shaping the government's decision-making. As the war progressed, there was growing support for direct U.S. involvement to defend democratic values and prevent the spread of totalitarianism.
These factors combined to lead the United States into World War II, shifting the balance of power and ultimately contributing to the Allied victory in 1945.