There are three. The sinking of the British liner Lusitania by German submarines that killed 128 US citizens, the Zimmermann telegram in which Germany promised aid for a Mexican invasion of the United States and the fact that if the Allied Forces lost, they wouldn't be able to pay back the money they borrowed from America.
The Lusitania and the Zimmerman Note
US got in the war because of the bombing in pearl harbor.
Only two states joined the U.S. during the American Civil War. West Virginia and Nevada joined during the war. Kansas joined on January 29, 1861 after secession began but before the war started on April 12, 1861.
to reorganize the union and to stop slavery from spreading but later on it was to abolish slavery completely.
The main opposition came from Copperheads, who were Southern sympathizers. Irish Catholics opposed the war due to the draft.
One of the main reasons that Us joined the war was due to there cruse ship being shot down by some of German submarines
it ended when the U.S. joined world war two
Germany & Italy
France and England, the Allies, later joined by the US
two years
The USA joined for two reasons. Firstly, the Japanese bombed an American naval base in Pearl Harbor (Hawaii). Secondly, they wanted to stop Hitler from eliminating the Jewish people.
The Lusitania and the Zimmerman Note
The answer to your question: 16,353,700 men & women served in the armed forces during World War Two.
US got in the war because of the bombing in pearl harbor.
It would be easier to name the countries which suceeded in remaining neutral in World War 2; Sweden, Switzerland, Ireland, Turkey, Spain, Portugal, Uruguay, and maybe a few others. All the rest eventually joined one side or the other, and some joined both sides. It was truly a world war.
World War I started when a Serbian assassinated the Franz Ferdinand, an Austrian archduke. Austria-Hungary declared war on Serbia. Russia, France, and Britain joined in on Serbia's side. Italy and Germany joined in on the Austria-Hungary side. World War II started when Germany invaded Poland and France. Britain declared war on Germany. The US entered later after Japan attacked the US at Pearl Harbor.
In World War I, the Central Powers were Germany, Austria-Hungary and the Ottoman empire. They were joined by Bulgaria in 1915. Italy refused to go to war despite the Triple Alliance, and later joined the Allies (the Entente Powers led by Great Britain, France, and Russia).