Czech, Polish, Slovak - Are These West Slavic Languages Pretty Much the Same?

Geographical Closeness and a Complicated History

The West group started separating from the other Slavic tongues at around the 7th century and the process lasted for quite a few hundred of years. Until then, there were fewer distinctions between the three subgroups, all of which are descended from the mythical ancestor of Proto-Slavic. Mythical because no actual writings in this language have been found, and it has been reconstructed by simply comparing the existing Slavic languages.