In 1660, the population of Jamaica was about 4,500 white and 1,500 black. By the early 1670s, as the English developed sugar cane plantations worked by large numbers of slaves, black Africans formed a majority of the population. The Irish in Jamaica also formed a large part of the island's early population, making up two-thirds of the white population on the island in the late 17th century, twice that of the English population. They were brought in as indentured labourers and soldiers after the conquest of 1655. The majority of Irish were transported by force as political prisoners of war from Ireland as a result of the ongoing Wars of the Three Kingdoms. Migration of large numbers of Irish to the island continued into the 18th century.