Complex sentence: Abdullah bin Sa'ad bin Abi'l Sarh was made the Governor of Egypt by his foster brother Caliph Uthman replacing Amr ibn al-Aas who had opposed naval warfare.
Split into simpler sentences: Abdullah bin Sa'ad bin Abi'l Sarh was the Governor of Egypt at the time. He had succeeded Amr ibn al-Aas who had opposed naval warfare.