The introduction of cash crops, particularly coffee, led to a series of changes in settlement patterns and social arrangements. But after a time, soil exhaustion, lack of support of African agriculture by the colonial authorities, incursions of Portuguese settlers who took over valuable property in the highlands, and a number of other factors contributed to a decline in the success of Ovimbundu cash-crop agriculture. By the early 1960s, up to 100,000 Ovimbundu, estimated at one-quarter of the group's able-bodied adult males, were migrating on one-year and two-year labor contracts to the coffee plantations of Uíge and Cuanza Norte provinces; another 15,000 to 20,000 sought work in Luanda and Lobito; and roughly the same number worked in the industrial plants of Huambo or for European farmers in the Benguela Plateau. In most cases, remuneration was low, but these migrant workers had little alternative. This pattern continued through the remainder of the colonial period, except for those males who were involved in nationalist activity (usually with UNITA).