Sinking of the Lusitania and breaking promises of un-restricted submarine warfare. Preventing U.S trade.
The US did not declare war on Germany in 1941, Germany declared war on the US as a measure of solidarity with Japan after their attack on Pearl Harbor and the Philippines.
Germany declared war on the United States on 11 December 1941 and the US responded accordingly.
The German telegram to Mexico and the sinking of U.S. merchant ships.
There has been military conflict between USA and Germany in two wars. In WWI it was USA declaring war on 6 April 1917. In WWII Germany declared war on 11 Dec 1941 as a response on USA's war declaration on their ally Japan on 8 Dec.
Because of the Japanese attack on Pearl Harbour in December 1941- Japan and Germany were allied by treaty, and the USA could not go to war against Japan without declaring war on Germany as well.
America declaring war on Nazi Germany and joining the Second World War in Europe.
11 December 1941
11 DECEMBER 1941 http://www.historyplace.com/worldwar2/timeline/germany-declares.htm Y-THINK-Y
mobilization
it became global
it became global
Japan attacked the US without Germany even knowing about it. Germany declared war on the US on December 11, 1941. Japan probably didn't even know about that until it happened. Hitler had invaded Russia in 1941 and no doubt was hoping Japan would open a second front on the Russians as a favor for him declaring war on America.