After World War I, Czechoslovakia established itself and as a republic and democracy with the establishment of the Constitution of 1920. The constitution was adopted by the National Assembly on 29 February 1920 and replaced the provisional constitution adopted on 13 November 1918.The constitution, modelled after constitutions of established democracies, was conceived in the light of Hans Kelsen's contribution to constitutional law. The system of government the constitution introduced made Czechoslovakia the most westernized of all of the central and eastern European nations on the verge of World War II.

The constitution created a parliament but also a president and cabinet, sharing powers of executive branch. Beneath them was a judiciary that was advanced with many levels of courts delegated for various types of cases.

Czechoslovakia, or Czecho-Slovakia (; Czech and Slovak: Československo, Česko-Slovensko), was a sovereign state in Central Europe, created in October 1918, when it declared its independence from Austria-Hungary.

In 1938, after the Munich Agreement, the Sudetenland became part of Germany, while the country lost further territories to Hungary and Poland. Between 1939 and 1945 the state ceased to exist, as Slovakia proclaimed its independence and subsequently the remaining territories in the east became part of Hungary, while in the remainder of the Czech Lands the German Protectorate of Bohemia and Moravia was proclaimed. In October 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, the pre-1938 Czechoslovakia was reestablished, with the exception of Carpathian Ruthenia, which became part of the Ukrainian SSR (a republic of the Soviet Union). From 1948 to 1989, Czechoslovakia was part of the Eastern Bloc with a command 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, known as the Prague Spring, was violently ended when the Soviet Union, assisted by some other Warsaw Pact countries, invaded Czechoslovakia. In 1989, as Marxist–Leninist governments and communism were ending all over Eastern Europe, Czechoslovaks peacefully deposed their socialist government in 17th November 1989 in the Velvet Revolution, state price controls were removed after a period of preparation. In 1993, Czechoslovakia split into the two sovereign states of the Czech Republic and Slovakia.