In 1914, Germany declares war on Russia, France and Belgium. Britain on Germany. Austria-Hungary on Russia. France and Britain on Austria-Hungary. Japan on Germany. While all of this is happening, the US is neutral
In 1914, Austria-Hungary declares war on Serbia.
Towards the end of 1914, Britain and France declare war on the Ottoman Empire
Midway through 1915, German U-boat torpedoes the Lusitania, a British passenger liner. 128 Americans are killed.
In March of 1917, British intelligence intercepts the Zimmermann Telegram, a secret communication from Germany proposing an alliance with Mexico should the United States enter the war.
In may of 1917, The U.S. Congress authorizes the Selective Service Act, initiating the first military draft since the Civil War