Complex sentence: Novgorod and Pskov escaped the Mongol yoke, however, and evolved into successful commercial republics; dozens of medieval churches (from the 12th century and after) have been preserved in these towns.
Split into simpler sentences: Novgorod and Pskov however managed to escape the Mongol yoke, and evolved into successful commercial republics. Many dozens of medieval churches, from the 12th century on, have been preserved in these towns.