The events of 1918, and the Peace Treaties of 1919 changed the map of Europe almost beyond recognition. The Peace treaties were very harsh for the Central powers. The harsh terms prevented notably Germany from rebuilding its national and economic life after the war. A state of affairs that contributed greatly to the frustration and anger of the Germans and the subsequent rise of the Nazi regime.

The three great Empires of Europe collapsed. In 1919 the Russian Socialist Federal Soviet Republic was declared. It joined in a formal confederation with other parts of the former Russian Empire in 1922, forming a state known to posterity as the Union of Socialist Soviet Republics, USSR or Soviet-Union. Finland and the Baltic states were lost to it. Poland declared war and defeated Russia. Poland expanded greatly beyond its original eastern border, the Curzon line.

After the German defeat the states that had formed on former Russian territory during the war dissolved their ties to Germany and, in the cases of Finland and Lithuania, annulled the succession of German Princes to their thrones. The Regency of the Kingdom of Poland, a German satellite state, stepped down in favour of a Republic led by Marshall Pilsudski.

The Dual Monarchy lost the war on the Italian front. It capitulated even before the Germans did. The Dual Monarchy could not survive this blow and the Emperor abdicated. The national aspirations of its many peoples, encouraged by the notion of the right of “self determination”, as put forward by the American President Wilson, resulted in the secession of the Czechoslovak Republic and the State of Slovenes, Croats and Serbs. With Austria the Peace of St. Germain was concluded. It was reduced to a rump-republic in German-Austria. South Tyrol was ceded to Italy, as were Istria and Triest. Poland received Galicia, and the Czechoslovak Republic was recognised. The State of Slovenes, Croats and Serbs joined Serbia in the new Kingdom of Serbs, Croats and Slovenes. The Buchovina was ceded Roumania. The remnant of Austria was forbidden to join Germany.

In Hungary a Republic was declared in 1918. The country was however reduced to chaos in the wake of the armistice agreements in which it was treated as one of the losing parties of the war, rather than as a new state seceded from the Dual monarchy, like Czechoslovakia was. Hungary had to give up Slovakia to the Czechoslovaks, Croatia and the Banat to the short-lived State of Slovenes, Croats and Serbs, and Transsylvania and adjacent lands to Roumania. In all of those territories large groups of ethnic Hungarians lived. The President, Count Karolyi, stepped down in protest and the government of the Magyar rump state was taken over by the Communists under the leadership of Bela Kun. This short lived Soviet state ended when the Roumanians intervened and occupied the country. The Kingdom was restored, but the King was not allowed to return, as the allies forbade the restoration of the Habsburg dynasty. Miklas Horthy takes over the government as Regent of a Kingdom with a vacant throne. The Peace of Trianon confirmed the territorial losses suffered by Hungary.

When the armistice had been conducted, Germany underwent a series of left-wing revolutions. The Emperor and King of Prussia abdicated. All other monarchs of German states followed suit. In Bavaria, a brief Communist revolution occurred. Social-Democrats took over the reins of power elsewhere. When a Communist revolution threatened Berlin, the Social-Democrat Chancellor Ebert, made a deal with the Army, and the "Spartakus revolution" was bloodily suppressed. Germany became a democratic Republic. Its constitution was agreed at Weimar, where a National Constituent Assembly gathered. The victorious powers however did not welcome the new German democracy (as the Viennese Congress had welcomed the restored Kingdom of France in 1814), but thoroughly humiliated it. The Peace of Versailles ceded large territories to Poland, notably a corridor that separated the province of East-Prussia from the rest of Germany. The port city of Danzig was made a free city, as was the Baltic port of Memel. France received Alsace-Lorraine back. Belgium and even neutral Denmark gained territory. The Danish speaking part of Schleswig (see 1861) was returned to Denmark. The Saar basin remained within the German Realm (as the Republic was still called) but was to be ruled by the League of Nations while France was given the exploitation of its mines. The Rhineland was occupied by the Allies, and later became a demilitarized zone. Germany was not allowed to have an army larger than a 100000 men, its Navy was decimated and there was to be no air force. Impossibly large reparations had to be paid. These payments were supposed to go on until the 1980’s. The payments were eventually stopped by the Conference of Lausanne in 1932. The Republic, which was forced to agree with these demands, never became popular with the humiliated German people.

With Ottoman Turkey, the Peace of Sevres was conducted. The Arabs, that had risen against the Turks in support of the British, were not given their independent states, but the territories were given to French and British rule as League of Nations mandates. Only the Hejaz became an independent Kingdom. The Turks lost East-Thrace and the Agean port of Smyrna and adjacent lands to the Greeks. In the East a short lived Armenian state was erected. The Sea straits area came under Allied occupation. The Italians occupied the area around Antalya, while the French occupied Cilicia. The national reconstruction movement of Turkey, originating in the Nineteenth Century revolution of the “Young Turks” gained momentum however. Under the leadership of Kemal Pasha, later known as Attatürk, the Turks fought successfully to revise the harsh terms of the Peace Treaty. In 1922 Sultan Mohammed VI abdicated, and his successor only took the subsidiary title of Caliph. In 1923 the Republic of Turkey is declared and the revision of the Sevres treaty is concluded in the Treaty of Lausanne. The French and the Italians had already left their occupied territories in 1921, and Turkey receives back Smyrna, East-Thrace and parts of French Syria. Armenia had already been split between Russia and Turkey in 1921. Armenians were again heavily persecuted, as they had already been earlier in the century. The Sea Straits were demilitarised and an international commission was to overlook free thoroughfare for all.

With Bulgaria the Treaty of Neuilly was conducted. King Ferdinand had resigned after the lost war, to save the throne for his successor King Boris III. Bulgaria had to cede some minor territories to the new Kingdom of Serbs, Croats and Slovenes, later known as Yugoslavia, and loses West-Trace to Greece.