The Porfiriato

The Porfiriato, 1876-1910. The first question to pose is why Mexico succumbed to a dictatorship and didn't achieve a liberal-democratic regime, since this is what most liberal politicians claimed they wanted. The answer has two sides to it:

(1) No representative political institutions were created by liberalism at local level. The regional caudillos remained firmly in control, and what Mexico had in the way of 'state institutions' were concentrated still in Mexico City. The liberal leadership simply joined the ranks of the existing landed oligarchy.

(2) The totally urban-based liberal political movement had done nothing to bring the agrarian masses into any form of participation in national life: indeed, liberalism created new types of rural unrest. This second point is particularly important. In the early decades of Independence, the different political  factions in Mexico tended to unite in the face of fear of popular rebellion and inter-class conflict. Those who were inclined to liberalism were too scared to rock the boat.

The constitutional republican state created by the liberals left private class power not simply untouched, but absolutely rampant. The only problem was that it was so weak and ineffective that it could not guarantee internal social tranquility or do anything about Mexico's 'national' problems - in particular the continuing threat posed by the USA to the country's national integrity. Díaz's regime offered an end to civil wars, greater social stability, and promised a form of national development: from the ruling class point of view it probably didn't matter too much that this national development involved the increasing domination of foreign capital initially, since the major problem through the 19th century had been the loss of national territory to the USA, and securing effective domination over the lower classes.
 
Díaz had been a liberal general, and in some ways he continued the trend set up by liberalism, particularly in the countryside. First of all, there's the question of Church-State relations. Díaz differed from his liberal predecessors, and the caudillos who ran the post-revolutionary state, particularly in the 1920s, by abandoning a strongly anti-clerical stance. It is extremely important to stress that the Church remained an independent corporate power in Mexican society after the Reform.  The Cristero rebellion reflected the fact that the Porfirian state had provided the conditions for the Church to recover its social power, so the struggle to do that had to be renewed under the post-revolutionary regime.  

Porfirio Díaz's attempt to create a stronger and more effective central state machine. At the start of Díaz's dictatorship, it was pretty evident that no Mexican government could afford to offend the landlord class in any way, and that power was effectively held by that class in a decentralized form in which whole areas of the country were effectively controlled by regional caudillos.
 
What Díaz did, in essence, was to try to beat the caudillos at their own game. He either coopted local strong-men and made them into his personal clients, or he inserted his own men as military or civil governors, so that they could control local opposition. His state still had very little in the treasury at first, so he was forced to rely on foreign capital to prop up this expanding structure of central patronage. He channelled money into infrastructural development railways, irrigation schemes, etc. - which increased the wealth of the landlord class, and landlords were supported by the state as they sort to take over peasant land and create a cheap rural proletariat.
 
He built up the federal army, and enormously enhanced the state's ability to collect taxes. Local communities which hadn't seen any manifestation of state power for decades now had to contend with recruiting sergeants and federal tax collectors. There was, therefore, some significant development of bureaucracy and a new  administrative apparatus under the regime, a siginificant degree of state 'modernization' and consolidation.  The weakness of the Porfirian state lay in the fact that its structure was held together by Díaz's personal  patronage system, and kinship relations among the Porfirian elite. Government had a tendency to remain arbitrary, not to mention corrupt.

But worse than that, Díaz failed to give any real thought as to how to replace his personal power and integrative function with institutions which would endure after he was gone: he simply refused to go, and he also refused to allow the Porfirian élite as a whole to steer his régime towards a more institutionalised and constitutional system. The Porfirian political system therefore created conditions for political crisis of the kind which could lead to social revolutionary crisis.