The Mexican Revolution that lasted from 1910 to 1920 was mainly caused by the desire of Mexicans for more democracy. Their country had experienced very little true democracy in its entire history. Since 1876, it had essentially been ruled by a dictator, Porfirio Diaz. By 1910, Diaz was old and had been showing signs of being willing to allow true democracy. When he failed to actually allow democracy, the revolution started.
When Mexico gained independence, it was first ruled by a self-styled “emperor.” After that, there was a long period of conflict in which various people took power, typically through military means. This included a time when the French allied with conservative Mexicans to put another monarch at the head of the Mexican government. In short, Mexico had very little democracy.
Then, in 1876, Diaz took power and ruled autocratically for more than 30 years. By the end of this time, it was the early 1900s and there was a feeling among many Mexicans that they should be able to have more democracy. This was what caused the revolution to start.