Protectorate of Bohemia and Moravia in the context of "Aktion T4"

Czechoslovakia (/ˌtʃɛkoʊsloʊˈvæki.ə, ˈtʃɛkə-, -slə-, -ˈvɑː-/ CHEK-oh-sloh-VAK-ee-ə, CHEK-ə-, -⁠slə-, -⁠VAH-; Czech and Slovak: Československo, Česko-Slovensko) was a landlocked country in Central Europe created in 1918 when it declared its independence from Austria-Hungary. In 1938, after the Munich Agreement, the Sudetenland became part of Nazi Germany. Between 1939 and 1945, the state ceased to exist, as Slovakia proclaimed its independence and Carpathian Ruthenia became part of Hungary, while the German Protectorate of Bohemia and Moravia was proclaimed in the remainder of the Czech Lands. In 1939, after the outbreak of World War II, former Czechoslovak president Edvard Beneš formed a government-in-exile and sought recognition from the Allies.

After World War II, Czechoslovakia was re-established under its pre-1938 borders, with the exception of Carpathian Ruthenia, which became part of the Ukrainian SSR (a republic of the Soviet Union). The Communist Party seized power in a coup in 1948. From 1948 to 1989, Czechoslovakia was part of the Eastern Bloc with a planned economy. Its economic status was formalized in membership of Comecon from 1949 and its defense status in the Warsaw Pact of 1955. A period of political liberalization in 1968, the Prague Spring, ended when the Soviet Union, assisted by other Warsaw Pact countries, invaded Czechoslovakia. In 1989, as Marxist–Leninist governments and communism were ending all over Central and Eastern Europe, Czechoslovaks peacefully deposed their communist government during the Velvet Revolution, which began on 17 November 1989 and ended 11 days later on 28 November when all of the top Communist leaders and Communist party itself resigned. On 31 December 1992, Czechoslovakia split peacefully into the two sovereign states of the Czech Republic and Slovakia.

The military occupation of Czechoslovakia by Nazi Germany began with the German annexation of the Sudetenland in 1938, continued with the creation of the Protectorate of Bohemia and Moravia, and by the end of 1944 extended to all parts of Czechoslovakia.

Following the Anschluss of Austria in March 1938 and the Munich Agreement in September of that same year, Adolf Hitler annexed the Sudetenland from Czechoslovakia on 1 October, giving Germany control of the extensive Czechoslovak border fortifications in this area. The incorporation of the Sudetenland into Germany left the rest of Czechoslovakia ("Rest-Tschechei" ) with a largely indefensible northwestern border. Also a Polish-majority borderland region of Trans-Olza which was annexed by Czechoslovakia in 1919, was occupied and annexed by Poland following the two-decade long territorial dispute. Finally the First Vienna Award gave to Hungary the southern territories of Slovakia and Carpathian Ruthenia, mostly inhabited by Hungarians.

Slovakia, officially the (First) Slovak Republic, and from 14 March until 21 July 1939 officially known as the Slovak State (Slovak: Slovenský štát), was a partially recognized clerical fascist client state of Nazi Germany which existed between 14 March 1939 and 4 April 1945 in Central Europe. The Slovak part of Czechoslovakia declared independence with German support one day before the German occupation of Bohemia and Moravia. It controlled most of the territory of present-day Slovakia, without its current southern parts, which were ceded by Czechoslovakia to Hungary in 1938. The puppet state was the first formally independent Slovak state in history. Bratislava was declared the capital city.

A one-party state governed by the far-right Hlinka's Slovak People's Party, the Slovak Republic is primarily known for its collaboration with Nazi Germany, which included sending troops to the invasion of Poland in September 1939 and the Soviet Union in 1941. In 1940, the country joined the Axis when its leaders signed the Tripartite Pact.

Reinhard Heydrich, the commander of the German Reich Security Main Office (RSHA), the acting Reichsprotektor of the Protectorate of Bohemia and Moravia and a principal architect of the Holocaust, was assassinated during the Second World War in a coordinated operation by the Czechoslovak resistance. The assassination attempt, code-named Operation Anthropoid, was carried out by resistance operatives Jozef Gabčík and Jan Kubiš on 27 May 1942. Heydrich was wounded in the attack and died of his injuries on 4 June.

The operatives who carried out the assassination were soldiers of the Czechoslovak Army who were prepared and trained by the British Special Operations Executive (SOE) with the approval of the Czechoslovak government-in-exile, led by Edvard Beneš. The Czechoslovaks undertook the operation to help confer legitimacy on the government-in-exile, and to exact retribution for Heydrich's brutal rule. The operation was the only verified government-sponsored assassination of a senior Nazi leader during the war. Heydrich's death led to a wave of reprisals by SS troops, including the destruction of villages and mass killings of civilians, including the Lidice massacre.

Reinhard Tristan Eugen Heydrich (/ˈhaɪdrɪk/; German: [ˈʁaɪnhaʁt ˈtʁɪstan ˈʔɔʏɡn̩ ˈhaɪdʁɪç] ; 7 March 1904 – 4 June 1942) was a high-ranking German SS and police official in Nazi Germany as well as one of the principal architects of the Holocaust. He held the rank of SS-Obergruppenführer und General der Polizei. Many historians regard Heydrich as one of the most sinister figures within the Nazi regime. Adolf Hitler described him as "the man with the iron heart."

Heydrich was chief of the Reich Security Main Office (including the Gestapo, Kripo, and SD). He was also Stellvertretender Reichsprotektor (Deputy Reich-Protector) of Bohemia and Moravia. He served as president of the International Criminal Police Commission (ICPC, now known as Interpol) and chaired the January 1942 Wannsee Conference which formalised plans for the "Final Solution to the Jewish question"—the deportation and genocide of all Jews in German-occupied Europe.

The Flensburg Government (German: Flensburger Regierung), also known as the Flensburg Cabinet (Flensburger Kabinett), the Dönitz Government (Regierung Dönitz), or the Schwerin von Krosigk Cabinet (Kabinett Schwerin von Krosigk), was the rump government of Nazi Germany during a period of three weeks around the end of World War II in Europe. The government was formed following the suicide of Adolf Hitler on 30 April 1945 during the Battle of Berlin. It was headed by Grand Admiral Karl Dönitz as Reichspräsident and Lutz Graf Schwerin von Krosigk as the Leading Minister. The administration was referred to as the "Flensburg Government" because Dönitz's command relocated to Flensburg in northern Germany near the Danish border on 3 May 1945. The sports school at the Mürwik Naval School was used as the government headquarters. The cabinet was not legitimised according to the Weimar Constitution, which was still formally in force.

At the time of its formation, forces loyal to the Nazi regime still held control of most of Austria and the Sudetenland, which was annexed by Germany in 1938. They also still controlled most of the Protectorate of Bohemia and Moravia which was partially annexed in 1939 when the remainder of Czechoslovakia was occupied, although after Hitler's death those Czech lands still occupied were effectively controlled by the SS with little meaningful oversight from Flensburg. Furthermore, the German military continued to occupy other non-German-speaking territories in disparate and isolated locations across Europe, such as Denmark, Norway, parts of the Netherlands, the Atlantic pockets in France and the British Channel Islands. However, in addition to losing most of its wartime conquests by this point, German forces had already been driven out of the vast majority of Germany's post-Anschluss territory, in addition to Luxembourg as well as the Polish and French territories Germany had either annexed or placed under direct German administration in the early stages of the war.