1918–1938: A democratic republic.
1938–1939: After annexation of Sudetenland by Germany in 1938, the region gradually turned into a state with loosened connections between Czech, Slovak, and Ruthenian parts. A large strip of southern Slovakia and Ruthenia was annexed by Hungary, and the Zaolzie region was annexed by Poland.
1939–1945: The region split into the Protectorate of Bohemia and Moravia and the Slovak Republic. A government-in-exile continued to exist in London, supported by the United Kingdom, United States and its Allies; after German invasion of Russia, it was also recognised by the USSR. Czechoslovakia was part of Declaration by United Nations and was a founding member of United Nations.
1946–1948: The country was governed by a coalition government with Communist ministers, with the prime minister and the minister of interior. Carpathian Ruthenia was ceded to the USSR.
1948–1989: The country became a communist state with a centrally planned economy. In 1960, the country officially became a socialist republic.
1969–1990: The federal republic consisted of the Czech Socialist Republic and the Slovak Socialist Republic.
1990–1992: The federal democratic republic consisted of the Czech Republic and the Slovak Republic.
I felt I had to deviate slightly from your text to make it sound right, otherwise it might sound as if it were written by a Russian:
"after THE German invasion of Russia.."
"part of THE Declaration by United Nations and was a founding member of THE United Nations"
"...a coalition government with Communist ministers, INCLUDING the prime minister and the minister THE of interior."
Also, for some reason unknown to me, we always say THE Sudetenland, but I missed that one.