Answer:
A. The United States winning the war and having a strong economy.
Step-by-step explanation:
The USA emerged as one of the great victorious powers of World War Two. Its soldiers fought in Asia, the Pacific and Europe, but not in the homeland. No battles ever took place on American soil. The war ended the Great Depression, the economy grew portentously , making the country reach its full industrial capacity and full employment. In 1945, the US economy represented 25% of the global GDP, more than another single country. So, the US became a world leader after WWII.