Despite cultural differences, the Slovaks share with the Czechs similar aspirations for independence from the Habsburg state and after the defeat of Austria-Hungary they voluntarily unite into Czechoslovakia (the Czechoslovak State). The country is later that year renamed Czechoslovak Republic. The incorporation of Slovakia in the new state is confirmed in the Treaty of Trianon in 1920. Czechoslovakia is a parliamentary democratic republic. Between 1918 and 1937 Tomáš Garrigue Masarýk is president. The first government is led by Karel Kramář of the Česka Státoprávní Demokracie (Czech Constitutional Democracy. ČSD) in an all-party coalition. He is succeeded in 1919 by Vlastimil Tusar of the Československá Sociálně Demokratická Strana Dělnická (Czechoslovak Social Democratic Workers' Party).
Since 1920 the governments are Czech dominated and mostly led by prime ministers from the Republikanská strana zemědělského a malorolnické lidu (Republican Party of Farmers and Peasants, RSZML, official name since 1922). These include Jan Cerný (1920-1921, 1926) and Antonín Švehla (1922-1926 and 1926-1929) and Frantisek Udržal (1929-1932), Jan Malypetr (1932-1935) and Milan Hodža (1935-1938). During this time the Slovenská L'udova Strana (Slovak People's Party, SLS) of Andrej Hlinka develops into the leading Slovak party. Masarýk is succeeded in 1937 by Edvard Beneš, until that time one of the leaders of the social-liberal Československá Národně Socialistická Strana (Czechoslovak National Socialist Party, ČNSS).
Although Czechoslovakia is the only East European country to remain a parliamentary democracy from 1918 to 1938, it is plagued with minority problems, the most important of which concerned the country's large German population. Constituting more than 22% of the interwar state's population and largely concentrated in the Bohemian and Moravian border regions (the Sudetenland), members of this minority, including some who are sympathetic to Nazi Germany, undermine the new Czechoslovak state. Internal and external pressures culminate in 1938, when France and the United Kingdom yieldeto Nazi pressures at Munich and agree to force Czechoslovakia to cede the Sudetenland to Germany. Beneš resigns and goes into exile. He is succeeded by Emil Hácha. The right-wing Czech parties merge into the Strana Národní Jednoty (National Unity Party, SNJ). This party strives after an authoritarian democracy and it can form the government under Rudolf Beran. Fulfilling Hitler's aggressive designs on all of Czechoslovakia, Germany invades what remains of Bohemia and Moravia in 1939, establishing the German "Protectorate of Bohemia and Moravia."
By this time, Slovakia has already declared independence and becomes a puppet state of the Germans. President of Slovakia becomes Jozef Tiso of the Hlinkova' Slovenská L'udova' Strana ((Hlinkov's People's Party, HSLS), the sole legal party. At the end of world war II, USSR troops overrun all of Slovakia, Moravia, and much of Bohemia, including Prague. Some parts of Bohemia are liberated by American forces.
When in 1945 Germany is defeated, Czechoslovakia is reconstituted and Edvard Beneš regains presidency. Following Germany's surrender, some 2.9 million ethnic Germans are expelled from Czechoslovakia with Allied approval under the Beneš Decrees. Reunited after the war, the Czechs and Slovaks set national elections for the spring of 1946. The democrats hope the USSR would allow Czechoslovakia the freedom to choose its own form of government and aspire to a Czechoslovakia that would act as a bridge between East and West. But in 1946 the Komunistická Strana Česk;eskoslovenska (Communist Party of Czechoslovakia, KSČ) wins the elections and holds most of the key positions in the government and gradually manage to neutralize or silence the anti-communist forces. In Slovenia the Demokratická Strana (Democratic Party, DS) becomes the largest party. Although the communist-led government under Klement Gottwaldinitially intend to participate in the Marshall Plan, it was forced by Moscow to back out. Under the cover of superficial legality, the KSČ assumes complete power in 1948. The DS is banned. From that time Czechoslovakia is a communist dictatorship under Klement Gottwald (1948-1953), Antonín Zápotocky (1953-1957) and Antonín Novotný (1957-1968). The country is renamed into Czechoslovak Socialist Republic in 1960.
In 1968 the Slovak reformist communist Alexander Dubček becomes leader of the KSČ. He wants to democratize society and starts a liberalization. His government takes practical steps toward political, social, and economic reforms. In addition, it calls for politico-military changes in the USSR-dominated Warsaw Pact and Council for Mutual Economic Assistance. The inititial reforms create great concern among some other Warsaw Pact governments. Later in 1968 USSR, Hungarian, Bulgarian, East German and Polish troops invade and occupy the country. This leads to the replacement of Dubček in 1969 by Gustav Husák.
Husák surrenders the party leadership in 1987 to Miloš Jakeš. Jakeš is replaced in 1989 by Karel Urbanék. The communist regime collapses at the end of 1989 when Husák is replaced as president by former dissident playwricht Václav Havel. In the transition period the country is renamed Czechoslovak Federal Republic. Later that year Czechoslovakia becomes a parliamentary democracy and is renamed Czech and Slovak Federal Republic. Marián Calfa of the Verejnost Proti Násiliu (Public against Violence, VPN) becomes prime minister. Dominating movement in the Czech part is the Občanské Fórum (Civic Forum, OF) and in Slovakia its counterpart VPN. Both movements are very heterogenous. The KSKSČ collapses. Both OF and VPN find however, that although they have successfully completed their primary objective, the overthrow of the communist regime, it is ineffectual as a governing party. The demise of both movements is viewed by most as necessary and inevitable.In 1992 a coalition of the conservative Občanská Demokratická Strana (Civic Democratic Party, ODS) and the Křestánska Demokratická Strana (Christian Democratic Party, KDS) becomes the largest party in the Czech part of the country and the Hnutie za Demokratické Slovensko (Movement for a Democratic Slovakia, HZDS) in Slovakia. Jan Stráský becomes federal prime minister, but real power in the Czech part of the country restst with Václav Klaus of ODS and in Slovakia with Vladimír Mečiar of the HZDS.
The federation is dissolved in 1993 and the country is seperated into the Czech Republic and Slovakia, officially named Slovak Republic. Slovakia becomes a parliamentary democracy, but in the first years of independence, the country is dominated by the authoritarian Movement for a Democratic Slovakia. This is interrupted by a reformist government under Jozef Moravcík in 1994. For the rest Slovakia is ruled by Mečiar's semi-authoritarian government that seriously breaches democratic norms and the rule of law until being ousted in the elections of 1998 by a coalition led by Mikulás Dzurinda. Despite a decline of the popularity of the governing parties, a last minute surge in support for Dzurinda's Slovenska Demokraticka a Krestanska Unia (Slovak Democratic and Christian Union, SDKU) enabales a coalition of his SDKU and the Magyar Koalíció Pártja (Hungarian Coalition Party, MKP), Krest'ansko-demokratické hnutie (Christian Democratic Movement, KDH) and the liberal Aliancia Nového Občana (New Civic Alliance, ANP). Slovakia joins the European Union in 2004.