A socialist revolution is rarely succinct or adhesive to a single strict ideological interpretation. When Mexico experienced its 1910 revolution, the rule of President Porfirio Díaz, the man the revolution formed to depose, came to an end early on. The bulk of the revolution’s decade long run consisted of violent infighting between the various socialist groups who struggled to assert their ideological interpretations over their fellow revolutionaries. Socialism appealed to many in Mexico as a great many Mexicans were landless peasant farmers or factory workers who were exploited by wealthy owners of capital. Led by revolutionaries like Emiliano Zapata, “…tens of thousands of peasants and workers asserted their claim to political participation by force,” but despite this social upheaval, much of Mexican societal organization remained in place. [1, 2] The landowners still owned the fields, and the capitalists still owned the factories.
By 1920 the infighting had lulled, and Mexico was governed under a new constitution that attempted to guarantee “…restrictions on clerical power, restoration of lands to deprived peasant communities, guarantees to labor…,” and an increase of state regulation over private enterprise.”  But these policies were ultimately compromises made in the face of the power of “…the old order…” comprising the small but wealthy ownership class that had lorded over the Mexican people since the nation’s independence.  Regardless of just how successful the revolution had been in uplifting the peasants and workers of Mexico, there still existed a general sense of victory amongst Mexican socialists, as can be seen in Diego Rivera’s Triumph of the Revolution, which celebrates the victory of Mexico’s revolutionaries over the destitute conditions that many of Mexico’s vulnerable faced. .
For the next few decades, the Mexican Left, defined by its democratic principles and socialist economics, held an effective monopoly over the government through the Partido Revolucionario Institucional (Institutional Revolutionary Party), as well as a variety of smaller regional parties.  During the early 1960s, many of these smaller left-wing political parties merged to form the Movimiento de Liberación Nacional (Movement of National Liberation) in opposition of the PRI. But the MLN did not last long as it fragmented within a few years of its formation. The breakdown of the movement resulted from ideological differences, such as disagreements over the sanctity of revolution and the limits revolutionaries should have in pursuing their goals to not violate their principles. This paper seeks to establish an understanding of how Mexican leftist ideology diverged into opposing camps during the 1960s and what this divergence represents in terms of ideological diversity and conflict.
Following Fidel Castro’s revolution in Cuba, a wave of renewed revolutionary fervor swept through many in Mexico who were dissatisfied by the administration of President López Mateos. After a general strike shut down Mexico City during the Easter weekend of 1959, Mateos deployed the military to end the strike, reassert state authority, and seize control of the railroad industry.  This authoritarian approach clashed with the pro-labor sentiment common within the Mexican Left, sparking an ideological push back from Mateos’ fellow socialists. Subsequently, the Mexican Left split into two factions: the Old Left and the New Left.  Taking inspiration from Cuba, “…the New Left came to be defined by an ideological belief in the validity and…necessity of armed insurrection as the strategy for sociopolitical renewal” in the face of government tyranny.  To effectively oppose Mateos and steer Mexico in their direction, the New Left formed the MLN. But while the New Left could find common cause against the authoritarianism of Mateos, ideological divides quickly sprung up between the members of the movement and like the Mexican Left as a whole, the New Left splintered into two groups which Eric Zolov, a professor of History at Stony Brook University and author of The Last Good Neighbor, describes as Vanguards and Cosmopolitans.
In Patrick Iber’s Neither Peace nor Freedom, he describes the divide that formed between the New Left as one over absolute loyalty to a revolutionary government and a commitment to ideological principles and “…the truth.”  The Cosmopolitans placed their principles before all else and welcomed criticism of their beliefs and self-reflection as tools to ensure the purity of their cause. Carlos Monsiváis, one of the foremost writers of the Cosmopolitans, declared that “the most urgent task facing Mexican intellectuals…” was to “…create and fortify in our country a critical perspective and a sense of humor.” [11, 12] Monsiváis was a revolutionary who pushed the bounds of cultural acceptability in his search for a more utopian model of society.  In this sense, the man served as an embodiment of the progressive and counterculture forces that drove the Cosmopolitan New Left. To Monsiváis, the route to a perfect society was one that challenged old doctrine and engaged with its ideological opponents, while valuing the intellectual freedoms of the individual. 
The Vanguards in turn represented a much more austere interpretation of revolution, that was “…characterized by a devout seriousness and reverence for the socialist cause.”  One Vanguard writer, Jean Franco, stated that “building a new society required discipline, not irony; hard work, not a freewheeling Bohemian style.”  To the Vanguard intellectual, the individual owed commitment to the revolution before all else and any activity that detracted from the revolution, or called it in to question, could not be allowed to stand. That is not to say the Vanguards were any less fervent in their criticism of the Old Left and desire to see a renewed socialist revolution in Mexico, but rather that the Vanguard comprised intellectuals “…who believed in the subordination of dissent to structural analysis,” that the irreverence of the Cosmopolitans should not be placed above enactment of socialist ideology.  The good of the cause came before the intellectual freedoms of the revolutionary.
By the mid-1960s, “the vision of a united Left, one which represented Mexico’s peasantry and working classes…had collapsed.”  Not only had the Mexican Left split into opposing factions, but one of said factions, the New Left, splintered as well. With the MLN shattered, Mateos and the PRI nominated their preferred candidate for the 1964 general election signaling a break between the government and the progressive forces sweeping through mid-twentieth century Mexico. The breakdown of the MLN illustrates divisions within socialist ideology over the role of the individual. Where the Cosmopolitans valued the individual and adherence to principles, the Vanguards valued the collective whole of the revolution and prioritized its enactment above all else. This divide between the importance of the individual and that of the collective was not a uniquely Mexican occurrence, but rather an extension of the same ideological battle that raged throughout the Cold War era.