Why did German think world war 1 was going to be a quick war (what was their plan, explain it, bonus if you can list what the plan was called)

Germany thought they could quickly defeat France, and then deploy their troop strength against Russia, whom Germany thought of as the bigger threat. The plan was called the Schlieffen Plan.

Explanation:

The military plans laid before World War I presupposed a war between the countries which were tied together with alliances. Because the Triple Entente had Britain, France and Russia as allies, Germany thought if a war began it would need to fight on two fronts - - west and east. So German Field Marshall Alfred von Schlieffen drew up war plans that said attack France first, quickly, and then hold that territory while deploying forces to contend with Russia in the east. In 1914, when Russia mobilized troops to come to the aid of Serbia against Austria-Hungary in 1914 (after the assassination of Austria's archduke by Serbian radicals), Germany declared war on Russia. And when Germany went to war, the first thing it did was to march through Belgium to go and attack France.

Germany's thought that they could quickly take control of France turned out to be quite wrong. The war on the western front with France bogged down, with each side digging into positions in trenches. The war dragged on for years with much death and little progress.