What series of events started WWI?

Serbia killed the king of Austria so that why austria declare war on servia. Russia got involved to defend Serbia. Germany seeing Russia defending Serbia, declared war on Russia. France was then drawn in against Germany and Austria. Germany attacked France through Belgium pulling Britain into war. Then Japan entered the war. Later, Italy and the United States would enter on the side of the allies.

All this countries got involved that´s why it was called a bloddy war.