World War II began in 1939 with the German invasion of Poland. It wouldn’t end for six years, ultimately claiming more than 50 million military and civilian lives, including 400,000 Americans. The United States, however, stayed out of the conflict until after Japan, allied with Germany, attacked Pearl Harbor in December 1941. The American public was initially divided over whether to enter the conflict. Interventionists, wanted America to enter the war on behalf of its allies. Isolationists, wanted to avoid a war waged on foreign soil. President Franklin Roosevelt began pushing the country away from isolation and neutrality, preparing the country for a war he felt was inevitable.

The Neutrality Acts

Many Americans considered World War I to have been a terrible mistake, too costly in both blood and treasure. By the 1930s, with the country gripped by the Great Depression, the U.S. Congress had staked out an isolationist position on foreign conflicts, even as Italy invaded Ethiopia, Japan conquered Manchuria and Germany began rapidly building up its military. In the mid-1930s, Congress passed the Neutrality Acts, which banned arms sales and loans to countries at war.

Lend-Lease

When Germany attacked Poland, kickstarting World War II, Roosevelt recognized the danger ahead. While still bound by the Neutrality Acts -- and campaigning for reelection on a promise not to enter the European conflict -- Roosevelt began seeking ways to provide America’s allies with assistance. This led him to push for a program called Lend-Lease, which would allow the president to ship weapons and other supplies to countries doing battle with Nazi Germany -- specifically, Britain, which was fending off the Germans. “The best immediate defense of Great Britain is the best defense of the United States,” Roosevelt told the nation, “and therefore that these materials would be more useful to the defense of the United States if they were used in Great Britain than if they were kept in storage here.”

The Debate Over Lend-Lease

Congress passed the Lend-Lease Act in 1941. Over the next four years, America sent more $50 billion of supplies to the Allies. The move was also perceived as an unofficial declaration of war against Germany. The materiel enabled Britain to resist Germany until America formally entered the war at the end of that year. Roosevelt and other interventionists argued that helping the British may actually prevent the U.S. from being drawn into war, while isolationists held that effectively taking sides made war more likely. The debate ended on December 7, 1941, when Japan bombed Pearl Harbor.

America Enters the War

Even before Congress passed the Lend-Lease Act, America had already begun readying its war machine. In 1940, Congress enacted the Selective Service Act, and the nation began drafting an army to take to war. The day after the Japanese attack, Congress declared war on Japan. Germany, Japan’s ally, then declared war on America. The war would last until 1945.