The major cause of the Mexican Revolution was the fact that Porfirio Diaz had been essentially the dictator of Mexico for more than 30 years.
In the 1900s, Diaz was getting old and people were worrying about what would happen after he died. Under pressure from advisers and from others, Diaz gave an interview to an American journalist in which he said that he would not run in the 1910 election and would allow the creation of an opposition party. In reaction to this declaration, Francisco Madero declared his candidacy for the presidency. When Madero started to get too popular, Diaz went back on his word and imprisoned him.
This was the basic background to the revolution. Mexicans wanted some amount of democracy after the long Porfiriato. They were promised some democracy in 1910. When that promise was broken, they rebelled against Diaz. This was the beginning of the revolution.