Complex sentence: The plague followed Golden Horde/Tatars from Sarai to Genoese merchants attacked in Tana, who fled to Caffa and by 1346 most of the Golden Horde settlements were affected by plague.
Split into simpler sentences: The plague followed Golden Horde/Tatars from Sarai to Genoese merchants attacked in Tana, who fled to Caffa. By 1346 most of the Golden Horde settlements were affected by plague.