Complex sentence: When Mahmud of Ghazni attacked Afghanistan and part of west India in the eleventh century, the destruction of the Buddhas and frescoes were beyond his understanding therefore he moved on to looting Buddhist monasteries and other important artifacts.
Split into simpler sentences: When Mahmud of Ghazni attacked Afghanistan and part of west India in the eleventh century, the destruction of the Buddhas and frescoes were beyond his understanding. Therefore he moved on to looting Buddhist monasteries and other important artifacts.