In 1945, at the Yalta Conference, in which the United States, England and the Soviet Union participated, it was agreed that Czechoslovakia became part of the Soviet orbit. The Red Army march to Prague in May of 1945, but before arriving and knowing the strength of the Czech people that the Soviets came from the east, they rebelled and managed to expel the Nazis one day before the Red Army entered the city. Liberated the Czechoslovak territory, it again became an independent state, but this time under the cloak of the Union of Soviet Socialist Republics (USSR). During this time large numbers of Germans and Hungarian collaborators were expelled.
In 1946, the Communist Party of Czechoslovakia (CCP) wins the elections with 36% of the votes. Czechoslovakia recovers the territories it had in 1918, except Ruthenia which is ceded to the USSR. President Beneš returns from exile and shares the government with the CCP, but due to lack of support, he resigned from office in 1948. The CCP began implementing reforms to adhere to Stalinist politics and promulgated a new constitution. Based on this, most of the political parties were declared illegal and the rest were subordinated to the CCP.  .
Towards 1956 the USSR undertook a demilitarization of the region and softened its policy. The political prisoners are released and in 1960 a new constitution is promulgated that turns Czechoslovakia into a socialist republic. In 1968, the Slovak Alexander Dubcek assumed the general secretariat of the CP and was elected president of the republic, and began a series of reforms, a fact known as the Prague Spring.
According to Topschoolsintheusa, the Warsaw Pact troops invaded Czechoslovakia, ending these reforms. Dubcek was detained and deported, and another 14,000 CCP officials were expelled from the party, and 500,000 of his followers lost their jobs.
Fall of communism
The opening and liberalizing winds from the Soviet Union through the so-called Perestroika, carried out by Mikhail Gorbachev as of 1985, took shape in all its allied countries with the beginning of gradual political reforms. In the case of Czechoslovakia we must go back to 1977, when a group of intellectuals, following the spirit of the Prague Spring, published a manifesto called “Letter 77”, in which they expressed their dissidence with the established government..
In 1989, the time of change in Europe, the people of Czechoslovakia knew about the fall of Soviet socialism and the fall of regimes in nearby countries through the radio (Radio Free Europe). On November 17 in Prague the police attacked thousands of students protesting against the communist government. This event caused the start of the demonstrations. After the creation of the Civic Forum directed by the playwright Václav Havel, and within the Czechoslovak Communist Party, power struggles were evident between immobile sectors such as Gustáv Husák and reformists such as Ladislav Adamec, which led to a climate of tension in the country.
With the general strike of the 27 of November of 1989 and the lack of support from its Soviet ally, the Czechoslovak Communist Party relinquished power. The hitherto champion of one-party orthodoxy, G. Husák, resigned on December 10 as President of the Republic. The events were precipitated and before the end of 1989 V. Havel acceded to the head of the State and Alexander Dubek to the presidency of the Parliament. In June 1990, new elections were held, from which the Civic Forum (Ob? Anské forum) and the Publicity Against Violence (Verejnos? Proti násiliu), a Slovakian variant of the first, would win.
Dissolution of Czechoslovakia
Before the 1990s, the per capita Gross Domestic Product of the Czech Republic was about 20% higher than that of Slovakia, but its lasting GDP growth was lower. Money transfers from the Czech budget to Slovakia, which had been the rule in the past, ceased in January 1991. Many Czechs and Slovaks wished for the continued existence of a federal Czechoslovakia. For their part, a slight majority of Slovaks advocated a more relaxed form of coexistence or complete independence.
In November 1992, a poll found that 49% of Slovaks and 50% of Czechs were against separation, while 40% of Slovaks supported it. The poll also found that 41% of Czechs and 49% of Slovaks thought the question should have been asked in a referendum. Ultimately, the fate of the country was decided by politicians. In 1992, the Czechs elected Václav Klaus and others who demanded an even stronger federation (viable federation) or, failing that, two independent states. Vladimír Meiar and other leading Slovak politicians at the time wanted a kind of confederation. The two sides engaged in frequent and intense negotiations in June. On July 17, the Slovak Parliament adopted the Declaration of Independence of the Slovak nation. Six days later
The objective of the negotiations changed, going to look for the way to reach a peaceful division. On November 25, the Federal Parliament adopted the Constitutional law marking the end of Czechoslovakia’s existence, which declared that from December 31, 1992 the Czech and Slovak Federal Republic would cease to exist, and provided the necessary technical details. The separation occurred without violence, and was so called: velvet divorce, in the image and likeness of the Velvet Revolution that had preceded it, which was carried out through mass demonstrations and peaceful actions, in contrast to the often violent disintegration of Yugoslavia and the Soviet Union. Both countries were admitted as members of the European Union in 2004.