Complex sentence: The first expedition under Robert Dudley and George Popham, who had waited and only departed from the area around 9 February but had captured many Spanish ships giving them an excuse to head back to England with their prizes.
Split into simpler sentences: The first expedition under Robert Dudley and George Popham, who had waited and only departed from the area around 9 February. Between them they had captured many Spanish ships giving them an excuse to head back to England with their prizes.