Complex sentence: The partition was generally supported by the Muslims of East Bengal by both their poor economic conditions in East Bengal and the perceived dominance of the Hindu businessmen and landlords in West Bengal over the governance of Bengal.
Split into simpler sentences: The partition was generally supported by the Muslims of East Bengal. Their support was motivated by both their poor economic conditions in East Bengal, as well as the perceived dominance of the Hindu businessmen and landlords in West Bengal over the governance of Bengal.