Czech Republic–Slovakia relations
Before 1918, both countries were part of Austria–Hungary. However, after the Ausgleich of 1867 Czechia belonged to the Austrian Empire while Slovakia belonged to the administratively separate Kingdom of Hungary, and between 1918 and December 31, 1992, both countries were part of Czechoslovakia. 
Both countries established diplomatic relations on January 1, 1993. These international relations are usually referred to or described as "very good", "cordial", and "above standard" in the media. When a Czech or Slovak president is inaugurated, very often his first international visit is to the former part of the common country. The same custom applies to newly elected prime ministers of the Czech Republic and Slovakia.
Origins of Czechoslovakia
Both Czechs and Slovaks struggled against a powerful neighbouring people; Germans in the case of the Czechs, Hungarians in the case of the Slovaks (see History of the Czech Republic and History of Slovakia). Contacts between the Czechs and Slovaks arose in the late fourteenth century, when Slovaks started to study at the University of Prague; in the fifteenth century, with the campaigns of the Czech Hussite armies to Slovakia; and in the seventeenth century, when Czech Protestants fled to Slovakia. Between the fifteenth and eighteenth centuries, some educated Slovaks used written Czech as well as Slovak and Latin (see History of the Slovak language). The Czechs and Slovaks were also formally united in 1436–1439, 1453–1457, and 1490–1918, when Hungary (which included Slovakia), Bohemia and other Central European states were ruled by the same kings.