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.
Czech Republic
The remaining Czech territory was occupied by Germany, which transformed it into the so-called Protectorate of Bohemia and Moravia. The protectorate was proclaimed part of the Third Reich, and the president and prime minister were subordinated to the Nazi Germany's "Reichsprotektor". Subcarpathian Rus declared independence as the Republic of Carpatho-Ukraine on 15 March 1939 but was invaded by Hungary the same day and formally annexed the next day. Approximately 345,000 Czechoslovak citizens, including 277,000 Jews, were killed or executed while hundreds of thousands of others were sent to prisons and Nazi concentration camps or used as forced labor. Up to two-thirds of the citizens were in groups targeted by the Nazis for deportation or death. One concentration camp was located within the Czech territory at Terezín, north of Prague. The Nazi "Generalplan Ost" called for the extermination, expulsion, Germanization or enslavement of most or all Czechs for the purpose of providing more living space for the German people.