Well, WW1 was technically started by Franz Ferdinand's Assassination. It was expanded from Austria-Hungary Vs. Serbia Because of the Numerous Guarantees of Sovereignty and Protections. It went in this Order. Austria Declares war on Serbia, Russia declares war on Austria, Germany Declares war on Russia, France Declares war on Germany, And finally, Germany Declares war on Belgium which Brings Britain into the Entente. And Further, the Ottomans and Bulgaria Joined the Central Powers, and Japan, Italy, and a few others Joined the Entente throughout the rest of the War.