Describe the causes of world war 1 and the events which led to the united states entering the war.

There are many causes that lead to WW1; Nationalism, imperalism, an arms race in europe but cheif among them was the assassination of Archduke Franz Ferdinand of Austria. The assasin was a serbian national so Austria blamed Serbia for it and declared war on them but serbia was in alliance with russia so russia came to serbia's defense which led to germany declaring war on russia which led great britan to declare war on germany. it just keeps going like that until all of europe is at war. 
the US went to war i think because the USS Lusitania got sunk by german U-boats which killed americans.