Native black warriors were employed in Africa by the Portuguese colonial rulers since the 16th century. Portugal had employed regular native troops ("companhias indigenas") in its colonial army since the early 19th century. After 1961, with the beginning of the colonial wars in its overseas territories, Portugal began to incorporate black Portuguese Africans into integrated units as part of the war effort in Angola, Portuguese Guinea, and Mozambique, based on concepts of multi-racialism and preservation of the empire. African participation on the Portuguese side of the conflict varied from marginal roles as laborers and informers to participation in highly trained operational combat units like the Flechas. As the war progressed, use of African counterinsurgency troops increased; on the eve of the military coup of 25 April 1974, black ethnic Africans accounted for more than 50 percent of Portuguese forces fighting the war.