It is divided into three branches: executive, legislative, and judicial, established by the Political Constitution of the United Mexican States, published in 1917.

The constituent states of the federation must also have a republican government based on a congressional system established by their respective constitutions.

Legislative power is vested in the Congress of the Union, a two-chamber legislature comprising the Senate of the Republic and the Chamber of Deputies.

[3] In 1920, a successful general in the Revolution named Alvaro Obregón overthrew the temporary government of the revolutionary leader Venustiano Carranza, which resulted in his election as the President of Mexico.

[7] The period from 1920–1934 in Mexico was marked by a strong presence of military in government and a failure to implement revolutionary reforms.

[8] Under President Lázaro Cárdenas (1934–40), the party transformed into the Partido de la Revolución Mexicana, which was organized on a corporate basis, with peasants, labor, the popular sector, and the military each having a division, with power centralized.

[11][12] During this time, the government nationalized key industries, such as oil, and implemented land reforms that redistributed property to peasants.

[15] However, the year 1982 gave way to market restructuring policies and gradual political reforms that prompted the democratic transition of Mexico (1982–2012).

Throughout the 20th century, the PRI had an almost hegemonic power at the state and federal levels, which slowly began to recede in the late 1980s.

[21] Even though since the 1940s, the PAN had won a couple of seats in Congress and its first presidential municipality (in Quiroga, Michoacán) in 1947,[22] it wasn't until 1989 that the first non-PRI state governor was elected (in Baja California).

Founded in 1929 as the Partido Nacional Revolucionario ("National Revolutionary Party"), the PRI dominated Mexican politics for over 70 years, bringing to power 11 different governments.

The PRD's beginnings date back to 1988 when dissident members of the PRI decided to challenge the leadership and nominated Cuauhtémoc Cárdenas for President of Mexico.

Morena grew out of a dispute between Andrés Manuel López Obrador and other PRD leaders after losing in the 2012 presidential election.

However, former President Andrés Manuel López Obrador's term only lasted five years and ten months (December 1, 2018 — September 30, 2024) due to a Constitutional change.

President Lázaro Cárdenas was fundamental to recovering some of the social control lost during the Revolution and the following economic meltdown in the United States.

Mexico was considered a bastion of continued constitutional government when coup d'états and military dictatorships were the norm in Latin America, in that the institutions were renovated electorally, even if only in appearance and with little participation of the opposition parties at the local level.

Some believed that Cardenas had won the election but that the then government-controlled electoral commission had altered the results after the infamous "the system crashed" (se cayó el sistema, as it was reported).

Although the opposition campaign was hurt by the desire of the Mexican electorate for stability, following the assassination of Luis Donaldo Colosio (the intended PRI candidate) and the recent outbreak of hostilities in the state of Chiapas, Zedillo's share of the vote was the lowest official percentage for any PRI presidential candidate up to that time.

Vicente Fox won the election with 42.5% of the vote, followed by PRI candidate Francisco Labastida with 36.1%, and Cuauhtémoc Cárdenas of the Party of the Democratic Revolution (PRD) with 16.6%.

Numerous electoral reforms implemented after 1989 aided in the opening of the Mexican political system, and opposition parties made historic gains in elections at all levels.

The court system was also given greatly expanded authority to hear civil rights cases on electoral matters brought by individuals or groups.

[27] On December 1, 2018, Andrés Manuel López Obrador was sworn in as Mexico's first leftist President in seven decades after winning a landslide victory in the 2018 election.

[36] In the 2021 midterm election, López Obrador's left-leaning Morena coalition lost seats in the lower house of Congress.

However, his ruling coalition maintained a simple majority, but López Obrador failed to secure the two-thirds congressional supermajority.