Complex sentence: The focus was initially on the well-known Indo-European languages, many of which had long written histories; the scholars also studied the Uralic languages, another European language family for which less early written material exists.
Split into simpler sentences: The focus was initially on the well-known Indo-European languages, many of which had long written histories. They also studied the Uralic languages, another European language family for which less early written material exists.