After the attack on the Archduke, Austria-Hungary blamed Serbia for the attack.
Two major events had caused the first world war.On July 28,1914 Austria-Hungary declares war on Serbia because of Archdukes assassination.This was the first day the war had begun. A few days later, on August the fourth 1914, Britian declares war on Germany. This is because Germany decided to invade France through Belgium.Britian was an ally with France so Britian had to do everything they could to protect France.These two events together are exactly how the first world war began.
ALLIANCES IN WW1 Alliances were used in the world war one with the Triple Entente which consisted of Britian,France and Russia.And the Triple Alliance which consisted of Germany,Austria-Hungary and Italy.Alliances were used when countries came together to achieve a specific goal.In this case the goal was to win the war.