Complex sentence: Pope's engineers cut a channel that allowed him to bypass the island, then, assisted by the gunboats of Captain Andrew H. Foote, he landed his men on the opposite shore, which isolated the defenders.
Split into simpler sentences: Pope's engineers cut a channel that allowed him to bypass the island. Assisted by the gunboats of Captain Andrew H. Foote, he landed his men on the opposite shore, which isolated the defenders.