World War I dismantled four empires and redrew nearly every border in Central and Eastern Europe. By the early 1920s, a series of peace treaties had erased the German, Austro-Hungarian, Ottoman, and Russian empires from the map and replaced them with a patchwork of new or expanded nation-states. The changes were enormous: entire countries appeared where none had existed, millions of people found themselves living under a different flag overnight, and the borders drawn during this period shaped European politics for the rest of the century.
Germany’s Shrinking Borders
The Treaty of Versailles, signed in June 1919, stripped Germany of 13 percent of its European territory, more than 27,000 square miles, and roughly one-tenth of its population, between 6.5 and 7 million people. The losses came from every direction.
To the west, France reclaimed Alsace-Lorraine, the industrially rich region it had lost to Germany in 1871. Belgium gained the small border districts of Eupen and Malmedy. The coal-rich Saar Basin was placed under League of Nations governance for 15 years, with France given full ownership of its mines as partial compensation for wartime destruction. After that period, residents would vote on which country they wanted to belong to. Meanwhile, the entire Rhineland, the strip of German territory west of the Rhine River, was demilitarized and occupied by Allied troops.
To the east, the changes were even more dramatic. A broad swath of territory, including the provinces of West Prussia and most of Posen, was transferred to the newly reconstituted state of Poland. This created the “Polish Corridor,” a strip of land 20 to 70 miles wide that gave Poland access to the Baltic Sea but physically separated the German region of East Prussia from the rest of Germany. The port city of Danzig (modern Gdańsk), though predominantly German-speaking, was not given to either country. Instead it became a “Free City” under League of Nations sovereignty. In the north, a plebiscite transferred part of Schleswig to Denmark.
The Breakup of Austria-Hungary
No empire’s collapse reshaped the map more thoroughly than Austria-Hungary’s. Before the war, the Habsburg monarchy controlled a vast stretch of Central Europe, from the Alps to the Carpathian Mountains. After the war, it simply ceased to exist. In its place emerged a collection of successor states, each one carved from former imperial territory.
Austria itself shrank to a small, landlocked, German-speaking republic, a fraction of its former size. Hungary’s losses were staggering. Under the Treaty of Trianon, signed in 1920, Hungary lost 71 percent of its territory and 64 percent of its population. Large portions of former Hungarian land went to Romania (Transylvania and surrounding areas), to the new Kingdom of Serbs, Croats, and Slovenes (later renamed Yugoslavia), and to Czechoslovakia.
Czechoslovakia was an entirely new creation, assembled from the Czech-speaking lands of Bohemia and Moravia plus the Slovak regions of former Hungary. Its borders also enclosed the Sudetenland, a mountainous rim populated by roughly three million ethnic Germans. This arrangement planted the seeds of a crisis that would erupt two decades later when Hitler demanded the Sudetenland’s return.
Poland, which had been partitioned out of existence in the late 1700s, reappeared on the map for the first time in over a century. It drew territory not only from Germany but from Austria-Hungary and the former Russian Empire.
A New Kingdom in the Balkans
The Balkans, already volatile before the war, were completely reorganized. As the Habsburg Empire disintegrated in 1918, its southern Slav minorities, including Croats, Slovenes, and Bosnians, sought union with Serbia. The result was the Kingdom of Serbs, Croats, and Slovenes, proclaimed in December 1918. This new state combined Serbia, Montenegro, and the former Austro-Hungarian territories of Croatia, Slovenia, Bosnia-Herzegovina, and parts of Dalmatia into a single, multiethnic country. In 1929 it officially adopted the name Yugoslavia.
Romania expanded significantly, gaining Transylvania from Hungary, Bessarabia from Russia, and parts of the Banat and Bukovina from Austria-Hungary. It roughly doubled in size. Bulgaria, which had fought on the losing side, was forced to cede territory to Greece, Romania, and the new Yugoslav state, losing its access to the Aegean Sea.
The Ottoman Empire’s Final Retreat
The Ottoman Empire had been losing European territory for decades, but the postwar settlement finalized the process. An initial treaty in 1920 (the Treaty of Sèvres) imposed harsh terms, but it was never fully implemented. After a war of independence led by Mustafa Kemal, Turkey negotiated the Treaty of Lausanne in 1923, which established the borders of the modern Republic of Turkey.
Under the Lausanne settlement, Turkey retained Eastern Thrace, the small but strategically important region near Istanbul on the European side of the straits. It also kept the Aegean islands of Gökçeada and Bozcaada, which sit near the Dardanelles and control access to key trade routes. Unlike the old Ottoman state, which had operated under various restrictions imposed by European powers, the new Turkey was recognized with full sovereignty. Thrace itself was divided three ways: eastern Thrace to Turkey, western Thrace to Greece, and a northern slice to Bulgaria.
The Baltic and Finland
The collapse of the Russian Empire, accelerated by the 1917 revolution and civil war, freed a tier of nations along the Baltic coast. Finland declared independence from Russia in December 1917. Estonia, Latvia, and Lithuania all emerged as independent states by 1920. These countries had been part of the Russian Empire for over a century, and their appearance on the map represented a completely new political reality along Europe’s northeastern edge.
Why the New Borders Caused Problems
The peacemakers at Versailles and the other conferences tried to follow the principle of national self-determination, the idea that ethnic groups should govern themselves. In practice, Central Europe’s populations were so intermixed that clean ethnic borders were impossible. Czechoslovakia included three million Germans. Romania’s new territories contained large Hungarian minorities. The Polish Corridor separated German communities from their national homeland. Yugoslavia combined Serbs, Croats, Slovenes, Bosnians, and others under one roof, with deep cultural and religious differences among them.
These mismatches meant that nearly every new state contained resentful minorities, and nearly every defeated power harbored ambitions to reclaim lost territory. Hungary’s loss of 71 percent of its land became a defining national grievance. Germany’s losses, particularly the Polish Corridor and Danzig, became rallying points for nationalist politicians. The map drawn after World War I lasted barely two decades before the unresolved tensions it created helped ignite a second, even larger conflict.