Krinay I don’t think you get it so after the assassination of arch duke frank Ferdinand Austro-Hungary declares war on Serbia thinking it won’t have a problem with such a small country but it does. After war is declared Russia declares war on austro-Hungary and comes to aid of Serbia but them Austria-Hungary gets backed by Germany and now Germany declares war on Russia and Serbia. So now Germany suspects France to get involved in the war so Germany plans to march to France and take Paris through Belgium but when German forces come into Belgium they are ordered to retreat by the British and so Germany refuses and Great Britain joins the war against Germany. soon after in the east the Ottoman Empire comes to the aid of Germany and Austro-Hungary and so causes the Arab revolt in the Middle East. And as time goes by other countries begin to join like Japan and Canada and even the US on April 6th 1917 after a German u-boat destroyed an American ship filled with American citizens. So now you know how it happened krinay goodnight