Here's why:
* Geographic Distribution: Slavic languages are spoken across a wide swathe of Eastern Europe, including countries like Russia, Poland, Ukraine, Belarus, Czech Republic, Slovakia, Slovenia, Croatia, Serbia, Bulgaria, and Macedonia.
* Number of Speakers: The Slavic languages have a large number of speakers, with Russian being the most spoken of the group.
* Historical Significance: The Slavic languages have a long and rich history in Eastern Europe, dating back to the early medieval period.
While Slavic languages are also spoken in parts of Central Europe and even in some regions outside of Europe, their concentration and influence are strongest in Eastern Europe.