World War II
The Allied economy and population compared with the Axis lessened with the early Axis victories. However, that was no longer the case after the United States and the Soviet Union joined the Allies in 1941. The Allies had a higher production level than the Axis because of more natural resources. Also, Germany and Japan did not plan for a long war and even had no ability to do so. Both tried to improve their economies by using slave laborers.