When and why did US join in second world war?

The United States joined World War II on December 7, 1941, following the Japanese attack on Pearl Harbor. This surprise military strike led to a significant loss of American lives and naval assets, prompting a declaration of war against Japan the next day. Subsequently, Germany and Italy declared war on the U.S., solidifying America's entry into the conflict. The U.S. aimed to combat the Axis powers and support its allies in restoring global stability and democracy.