Complex sentence: The Tatars first reached the mouths of the Danube in the mid- 13th century at the height of power of the Golden Horde and in 1241, under the leadership of Kadan, the Tatars cross the Danube and conquer and devastate the region.
Split into simpler sentences: The Tatars first reached the mouths of the Danube in the mid- 13th century at the height of power of the Golden Horde. In 1241, under the leadership of Kadan, the Tatars crossed the Danube, conquering and devastating the region.