Complex sentence: The 16th century English conquest of Ireland was made piece by piece and begun in the reign of Henry VIII (1509--1547); it was completed after sustained warfare in the reign of Elizabeth I (1558--1603).
Split into simpler sentences: The 16th century English conquest of Ireland was made piece by piece. It began under the authority of King Henry VIII (1509--1547) and came to an end after sustained warfare, in the oversight of Elizabeth I (1558--1603).