Original sentence: national security doctrine and the fear of a domino effect of left-wing, marxist regimes taking control in Central America was the reason the U.was a strong supporter of El Salvador's ruling class
Edited sentence: national security doctrine ([[Central America as  US patio) and the fear of a domino effect of left-wing, marxist regimes taking control in the area were the reasons the US were strong supporters of the ruling class in El Savador