You killed our heir the throne! We will go to war!
Fine. *whispers* But we are soooo better than you.
Austria-Hungary, Italy, and Germany (Central Powers)
Let's make an alliance. Then we will go to war!
Serbia, Russia, Great Britain, and France (Allied Powers)
GAAAH! WE SURRENDER!!!
After their victory in WW1, the Allied Powers wrote up the Treaty of Versailles.
It stated that Germany MUST accept blame for starting the war, cut the size of its army, and give up its oversea colonies as well as pay for all damages.
After the war was over, there were some changes in Russia. The war caused hardships for people, and Vladimir Lenin brought communism to Russia, where the government owns all property and controls all aspects of life.
But Russia wasn't the only thing that changed. Austria and Hungary became separate countries, countries gained independence, and some countries became independent.