Complex sentence: The 16th century English conquest of Ireland was made piece by piece and starting in the reign of Henry VIII (1509--1547) and only being 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 Queen Elizabeth I (1558--1603).