The dominant political party in Mexico for most of the 20th century was

Ans: The Institutional Revolutionary Party (Spanish: Partido Revolucionario Institucional; abbr. PRI) is a political party in Mexico that was founded in 1929 and held uninterrupted power in the country for 71 years, from 1929 to 2000, first as the National Revolutionary Party (Spanish: Partido Nacional Revolucionario, PNR), then as the Party of the Mexican Revolution (Spanish: Partido de la Revolución Mexicana, PRM) and finally as the PRI beginning in 1946.

They made a checks and balance system to equal power within the branches. the "check" meant that one branch would watch one branch and "balance" them if they were too powerful. if you want more info on this, i would just google checks and balance system.