Complex sentence: During the 17th century, an estimated 350,000 English and Welsh migrants arrived as permanent residents in the Thirteen Colonies, which in the century after the Acts of Union 1707, was surpassed in rate and number by Scottish and Irish migrants.
Split into simpler sentences: During the 17th century, an estimated 350,000 English and Welsh migrants arrived as permanent residents in the Thirteen Colonies. In the century after the Acts of Union 1707 this was surpassed in rate and number by Scottish and Irish migrants.