As the war progressed, Portugal rapidly increased its mobilized forces. Under the Salazar regime, a military draft required all males to serve three years of obligatory military service; many of those called up to active military duty were deployed to combat zones in Portugal's African overseas provinces. The national service period was increased to four years in 1967, and virtually all conscripts faced a mandatory two-year tour of service in Africa. The existence of the draft and likelihood of combat in African counterinsurgency operations would over time result in a sharp increase in emigration by Portuguese men seeking to avoid such service. By the end of the Portuguese colonial war in 1974, black African participation had become crucial due to declining numbers of recruits available from Portugal itself.