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
On May 31, 1918, Czech and Slovak representatives in the United States signed the Pittsburgh Agreement endorsing a plan for a unified Czecho-Slovak state in which Slovakia would have its own assembly. In early October 1918, Germany and Austria proposed peace negotiations. On October 18, while in the United States, Masaryk issued a declaration of Czechoslovak independence. Masaryk insisted that the new Czechoslovak state include the historic Bohemian Kingdom, containing the German-populated borderland. On October 21, however, German deputies from Bohemia joined other German and Austrian deputies in the Austrian parliament in declaring an independent German-Austrian state. Following the abdication of Charles I on November 11, Czech troops took control of borderlands.