Explain why the USA did not enter the Second World War until December 1941.

When addressing questions like this, it's very important not to simply describe why the USA did not enter the Second World War until 1941. Normally, to unpack questions like this, its important to think of the three main factors which you think are the most important, and justify why they all relate back to and answer the question. For high level answers, you need to argue why these factors link together. (Remember, in History, events rarely happen on their own, there are always many factors that are influencing). 

Firstly, and most importantly, you have to begin the answer to this question with an awareness of US ideology; Isolationism. The USA had a strong sense of isolationist feeling, and had done for decades. This was especially strong in congress. You also have to mention that the USA had a 'never again' feelings, especially after its involvement in the First World War. American families didn't want US soldiers to be fighting in a war that was so far away from home. This is a huge factor explaining why the USA didn't enter WWII until 1941. 

Secondly, because of the isolationist feeling that was popular in America, you have to explain that Roosevelt was conscious about getting re-elected. If he agreed to sign up America to the war effort, he could become unpopular. The main rhetoric that FDR employed in his campaign for re-election in 1940 (its important to remember this date), was that he "would not send our boys" to fight in another states' war. You could explain here that because FDR was re-elected in 1940, the USA did not enter until 1941, when he had run his election campaign and won anyway. 

Thirdly, you need to acknowledge American immigration that had been happening since 1990. There were many German and Irish migrants in the US, who not only didn't want to help Britiain, but didn't want their new homeland to go to war against their old homelands. This is a huge acknowledgement to American history, and its important to show the examiner that you understand the different influences in civil society, not only in their voting patterns, but also in their heritage and what they were contributing to American Industry and society as new settlers.