The rise of Soviet influence in the working class , and the cost of the Portuguese Colonial War ( 1961 â `` 1974 ) , led to its failure in 1974 . The rise of Soviet influence among the Movimento das ForÃ as Armadas 's military ( MFA ) and working class , and the cost and unpopularity of the Portuguese Colonial War ( 1961 â `` 1974 ) , in which Portugal resisted to the emerging nationalist guerrilla movements in some of its African territories , eventually led to the collapse of the Estado Novo regime in 1974 .