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.
World War II by country
The newly separated Slovak Republic (1939–1945), led by Jozef Tiso was set up in Slovakia. Part of southern Slovakia and all of Ruthenia (the former eastern end of Czechoslovakia) was annexed by Hungary. Zaolzie was annexed by Poland, snatched from them by the Germans 11 months later, and returned to Czechoslovakia in 1945 by the Soviet Union. The Slovak National Uprising, commenced in August 1944, was suppressed by German forces at the end of October; partisans, however, continued fighting in the mountains until the war's end. In April 1945, the Red Army defeated the Germans and ousted Tiso's government, annexing Carpathian Ruthenia to the USSR.