villages. Throughout the 16th century, Ulster was viewed by the English as being "underpopulated" and undeveloped. The economy of Gaelic Ulster was overwhelmingly based on agriculture, especially cattle-raising. Many of the Gaelic Irish practiced "creaghting" or "booleying", a kind of transhumance whereby some of them moved with their cattle to upland pastures during the summer months and lived in temporary dwellings during that time. This often led outsiders to mistakenly believe that the Gaelic Irish were nomadic. Michael Perceval-Maxwell estimates that by 1600 (before the worst atrocities of the Nine Years' War) Ulster's total adult population was only 25,000 to 40,000 people. Others estimate that Ulster's population in the year 1600 was about 200,000. The wars fought among Gaelic clans and between the Gaelic and English undoubtedly contributed to depopulation. The Tudor conquest of Ireland began in the 1540s during the reign of Henry VIII (1509–1547) and concluded in the reign of Elizabeth I (1558–1603) sixty years later, breaking the power of the semi-independent Irish chieftains. As part of the conquest, plantations (colonial settlements) were established in Queen's County and King's County (Laois and Offaly) in the 1550s as well as Munster in the 1580s, although these were not very successful. In the 1570s, Elizabeth I authorized a privately funded plantation of eastern Ulster, led by Thomas Smith and Walter Devereux, 1st Earl of Essex. This was a failure and sparked violent conflict with the local Irish lord, in which Lord Deputy Essex killed many of the lord of Clandeboy's kin. In the Nine Years' War of 1594–1603, an alliance of northern Gaelic chieftains—led by Hugh O'Neill of Tyrone, Hugh Roe O'Donnell of Tyrconnell, and Hugh Maguire of Fermanagh—resisted the imposition of English government in Ulster and sought to affirm their own control. Following an extremely costly series of campaigns by the English the war ended in 1603 with the Treaty of Mellifont. The terms of surrender granted to what remained of O'Neills rebels were considered generous at the time. After the Treaty of Mellifont, the northern chieftains attempted to consolidate their positions, whilst some within the English administration attempted to undermine them. In 1607, O'Neill and his primary allies left Ireland to seek Spanish help for a new rebellion to restore their privileges, in what became known as the Flight of the Earls. King James issued a proclamation declaring their action to be treason, paving the way for the