The United States entered the Second World War in December of forty-one. Europe had already been at war since nineteen thirty-nine.But the United States did not enter World War Two until Japanese forces attacked the American naval base at Pearl Harbor, Hawaii.The attack was a surprise.But American military and political leaders had believed that the United States, sooner or later, would be pulled into the fighting.And they began to prepare for war.President Franklin Roosevelt had been assistant secretary of the Navy under President Woodrow Wilson during World War One.He remembered how American troops were not ready for that war.Now that he was president, Roosevelt wanted to be sure that the United States would be ready when it had to fight.Throughout nineteen forty-one, Roosevelt urged American industries to produce more weapons and other military supplies.He established new government agencies to work with industry to increase arms production.