Complex sentence: The years of Oliver Cromwell's Puritan rule were a bad time for the theater, altogether outlawed also in England itself; and Ireland, conquered by Cromwell's troops, suffered various kinds of harsh oppression.
Split into simpler sentences: The years of Oliver Cromwell's Puritan rule were a bad time for the theater, altogether outlawed also in England itself. Moreover, Ireland, conquered by Cromwell's troops, suffered various other kinds of harsh oppression.