There are almost 5 million first-language speakers of Slovak, in at least 130 territories. The vast majority are in Slovakia, around 200 thousand are in the Czech Republic, and the remainder are in other European territories and the United States.
Slovak and Czech are mutually intelligible, and might be considered to be dialects of the same language. Their influence on each other predates the creation of Czechoslovakia.
Territory size shows the proportion of all people who speak Slovak as a first language that live in that territory.