The Mexican Revolution.
The Mexican Revolution was a major armed struggle that started in 1910, with an uprising led by Francisco I Madero against longtime autocrat Porfirio Diaz, and lasted for the better part of a decade until around 1920. Over time the Revolution changed from a revolt against the established order to a multi-sided civil war. This armed conflict is often categorized as the most important sociopolitical event in Mexico and one of the greatest upheavals of the 20th century.
After prolonged struggles, its representatives produced the Mexican constitution of 1917. The Revolution is generally considered to have lasted until 1920, although the country continued to have sporadic, but comparatively minor, outbreaks of warfare well into the 1920. The Cristerio War of 1926 to 1929 was the most significant relapse into bloodshed.