Czechoslovakia faced significant upheaval during World War II, beginning with its partition and occupation by Nazi Germany. After the Munich Agreement in 1938 forced Czechoslovakia to cede the Sudetenland to Germany, a heavily German-populated border region, the state’s defenses were critically weakened. Soon after, in March 1939, the German Wehrmacht invaded, and Hitler declared the Protectorate of Bohemia and Moravia, placing the remainder of the Czech lands under German control. Slovakia broke away as a separate puppet state, and Carpathian Ruthenia was annexed by Hungary.
Under Nazi rule, Czech industry, especially the Škoda Works, was retooled to support the German war machine, producing weapons and supplies essential to the Nazi military. Many Czechs were forced into labor, either in Germany or locally to support the occupation. Harsh reprisals were enforced, with around 300,000 Czechs, primarily Jews, perishing. The occupation intensified in 1942 after the assassination of Reinhard Heydrich, the acting Reich Protector and one of the architects of the Holocaust, by Czech resistance fighters. In retaliation, German forces destroyed the villages of Lidice and Ležáky, killing most of their residents.
A Czech government-in-exile, led by former President Edvard Beneš, operated from London, coordinating resistance and working for the Allies' support. In 1942, the exiled government gained recognition and repudiation of the Munich Agreement. Resistance within Czechoslovakia included both underground networks and armed partisan groups, which escalated guerrilla activity as the war continued. In 1944, the Slovak National Uprising sought to overthrow the Nazi-aligned Slovak government but was ultimately suppressed.
The end of Nazi occupation came in May 1945, when Soviet forces liberated Prague. Following the war, the Czechoslovak government returned, and Edvard Beneš signed the decrees for the expulsion of the ethnic German population from Czechoslovakia, leading to the forced relocation of millions. Subcarpathian Ruthenia was ceded to the Soviet Union, and postwar Czechoslovakia aimed to reestablish itself as a unified state, though deeply scarred by occupation, conflict, and ethnic division.