Post your question again, please, and tell us which war you are thinking of.
America declaring war on Nazi Germany and joining the Second World War in Europe.
The unprovoked attack by the Japanese on Pearl Harbour
Usually, the government of the country is responsible for declaring war. In the United States of America, the Department of Defense is responsible for declaring wars.
The incident that led to congress declaring war on Spain was the Maine incident. The war cry was remember the Maine. The sinking of the U.S. battleship Maine in Havana harbor.
Germany declared war on Poland, which led to England and France declaring war on Germany.
The Sinking of the USS Maine.
The U.S. was pissed of at Japan in WW2 because the Japanese attacked Pearl Harbour (a U.S base) un-provoked, which led to the government of America declaring war on Japan
The German telegram to Mexico and the sinking of U.S. merchant ships.
The incident that led to congress declaring war on Spain was the Maine incident. The war cry was remember the Maine. The sinking of the U.S. battleship Maine in Havana harbor.
America colonist proclaim declaring independence because of the war. The war was so that we could have freedom.
Germany allied with Japan, Japan attacked America Germany had no choice and Hitler was not happy as he wanted to keep America out of the war.
The immediate cause was Japan's attack on Pearl Harbor. This caused the US to declare war on Japan, which led to Germany and Italy declaring war on the US.