Bohemia is the westernmost and largest historical region of the Czech lands in the present-day Czech Republic. In a broader meaning, Bohemia sometimes refers to the entire Czech territory, including Moravia and Czech Silesia, especially in a historical context, such as the Lands of the Bohemian Crown ruled by Bohemian kings. 

Bohemia was a duchy of Great Moravia, later an independent principality, a kingdom in the Holy Roman Empire, and subsequently a part of the Habsburg Monarchy and the Austrian Empire. After World War I and the establishment of an independent Czechoslovak state, Bohemia became a part of Czechoslovakia. Between 1938 and 1945, border regions with sizeable German-speaking minorities of all three Czech lands were joined to Nazi Germany as the Sudetenland. 

The remainder of Czech territory became the Second Czechoslovak Republic and was subsequently occupied as the Protectorate of Bohemia and Moravia, In 1969, the Czech lands (including Bohemia) were given autonomy within Czechoslovakia as the Czech Socialist Republic. In 1990, the name was changed to the Czech Republic, which become a separate state in 1993 with the dissolution of Czechoslovakia. Until 1948, Bohemia was an administrative unit of Czechoslovakia as one of its "lands" ("země"). Since then, administrative reforms have replaced self-governing lands with a modified system of "regions" ("kraje") which do not follow the borders of the historical Czech lands (or the regions from the 1960 and 2000 reforms). However, the three lands are mentioned in the preamble of the Constitution of the Czech Republic: "We, citizens of the Czech Republic in Bohemia, Moravia and Silesia…"
What happened to Czechoslovakia at that time?
dissolution