What was the main reason for the Allies' decision to defeat Germany and Italy before defeating Japan?

Europe first, also known as Germany first, was the key element of the grand strategy agreed upon by the United States and the United Kingdom during World War II. According to this policy, the United States and the United Kingdom would use the preponderance of their resources to subdue Nazi Germany in Europe first. Simultaneously, they would fight a holding action against Japan in the Pacific, using fewer resources. After the defeat of Germany-considered the greatest threat to the UK[1]-all Allied forces could be concentrated against Japan.

At the December 1941 Arcadia Conference between President Franklin Roosevelt and Prime Minister Winston Churchill in Washington, shortly after the United States entered the War, the decision for the "Europe First" strategy was affirmed. However, U. S. statistics show that the United States devoted more resources in the early part of the war to stopping the advance of Japan, and not until 1944 was a clear preponderance of U. S. resources allocated toward the defeat of Germany.