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.
Kadaň
In the final weeks of World War I, Czechoslovakia was established on 28 October 1918, its Bohemian, Moravian and Silesian component having been defined by the historic borders of the Czech (Bohemian) kingdom. However, most of the German border population, was not enthusiastic about becoming part of a new republic with a clearly Slavonic definition. Instead, four regional self-governed states emerged along the borderland, according to the right for self determination guaranteed by Woodrow Wilson in no. 10 of his Fourteen Points. Kaaden, (Kadaň in Czech), declared itself part of German Bohemia. On 4 March 1919, the first assembly of the German Austrian parliament was the occasion for both peaceful and violent demonstrations in the mostly German-populated border cities. In Kadaň, the curfew and martial law was declared and the Czechoslovak military forces were sent in. The demonstration in Kadaň for self determination was the bloodiest. According to Swiss Neue Zürcher Zeitung report of 7 March 1919, 17 persons were killed, 30 badly wounded, and 80 wounded there. Over all, 25 victims were buried in a memorial grave at the central cemetery. It was restored after the fall of communism in 1989.