Зачем америка вступила в 2 мировую войну?

This means 'Why did America step into the second world war?'.

The answer is because 'The Americans were forced to join WWII because the Japanese Navy and Air Forces bombed Pearl Harbor on Sunday, Dec 7, 1941. On Monday, Dec 8, 1941, America declared war on Japan. Three days later Germany declared war on the USA.'