World War 1 began with an alliance called the "Triple Entente" which consisted of Britain, France, Ireland, and Russia.
What triggered the war to start was the assassination of Archduke Franz Ferdinand in Sarajevo. Weeks after the countries were at war.
Its not determined who really started the war but that is what lit the fuse.
Hope this helps!
Brainliest is always appreciated if you feel its deserved!
