Slovak is a Western Slavonic language spoken by about 5.6 million people in Slovakia and also in Canada, Hungary, Poland, Romania, Ukraine and the USA. Slovak is closely related to Czech, Polish, and Sorbian.
Documents in Slovak started to appear in the 15th century, however a widely accepted literary standard for Slovak did not emerge until the 19th century. Slovak literature flourished between 1918 and 1938 when the Slovak-speaking area became part of Czechoslovakia, though the Czech majority did not all recognise the separate status of the Slovak language.
Since the demise of Czechoslovakia in 1993, Slovakia has been an independent country and the Slovak and Czech languages have started to drift away from each other, though they are still more or less mutually intellegible.
source
wikipedia.org,
omniglot.com,
evertype.com &
ethnologue.com