hubieran marcado
-they/you had marked
Antecopréterito de subjuntivo para el sujetoellos/ellas/ustedesdel verbomarcar.

marcar

Y si a las derrotas de las primeras experiencias socialistas les hubieran seguido nuevos triunfos de establecer o reestablecer la dictadura del proletariado, esas derrotas tal vez no hubieran marcado el fin de la primera etapa.
And if the defeats of the first socialist experiences had been followed by new victories in establishing or reestablishing the dictatorship of the proletariat, these defeats might not have marked the end of the first stage.
Palabra del día
el portero