Complex sentence: Docwra had returned to England with Essex in the autumn of 1599: in 1600 hewas sent back to Ireland as commander of an army of 4000 men and captured the ruined site of Derry in May 1600.
Split into simpler sentences: Docwra had returned to England with Essex in the autumn of 1599. I n 1600 he was sent back to Ireland as commander of an army of 4000 men and captured the ruined site of Derry in May 1600.