There had been tensions all over Europe before WWI started. What really started this though was when Archduke Franz Ferdinand was shot by a Serbian nationalist. After this many countries started blaming the Serbian Government. Serbia backed to Russia because they were convinced that Austria-Hungrey was going to attack. When the attacks started this led to the downfall of Europe's great powers. There were two sides fighting, they were the Central powers made up of Bulgaria, and the Ottoman Empire, which supported Germany and Austria-Hungrey. The Allies were Russia, France, Belgium, and Great Britain. They were later joined by the U.S. which played a very big role, and China, Romania, and Japan. This event is very important because it ended four major European dynasties. It also laid the groundwork for WWII. It also started making many new countries from what was before. Finally, it changed views on politics, culture and society.