Complex sentence: However, he was appointed to fortify the island of Mala Khortytsia on the Dnipro beyond the rapids, a task he did so thoroughly that khan Devlet I Giray could not take it, and deflected khan's efforts to Moskovia.
Split into simpler sentences: However, he was appointed to fortify the island of Mala Khortytsia on the Dnipro beyond the rapids. Eventually he managed to develop to the point that khan Devlet I Giray could not take it, and deflected khan's efforts to Moskovia.