World War II started when Germany, Italy, and Japan declaring war on the Allies powers.
At the beginning of the war, the Axis powers didn't declare on the U.S so the people didn't want to participate in a war that wasn't for them.
We don't want to die in a war that wasn't originally for us.
We, the government, would like to inform you that we won't be participating in the Second World War, due to the lack of support and official war declaration from the Axis.
President Roosevelt of the United States of America
We can try to send something but you need to collaborate.
Due to the fact that Britain was an ally of the U.S and they can stop Hitler from crossing the Atlantic Ocean, President Roosevelt had decided help them.
We need help! If you can't send troops then could you send supplies and weapons?
Despite Congress's previous neutrality act to keep us out the war, the government had a meeting to pass a new act to allow the Allies to buy arms from us if they paid cash and carried them in their own ships.
But since we are allies with the U.K, a lend-lease act that will allow them to purchase our weapons without immediate payments and a group to convoy British ships part of the way across the Atlantic may also be formed if the war continue negatively.