By the turn of the 20th century, there was talk of abolishing the Rangers. The frontier had been tamed, and the Rangers seemed little more than a relic of earlier, more colorful times. Then came the Mexican Revolution. From 1910-1920, Mexico endured the misery of violence and civil war, and the border country of Texas was soon swept into the maelstrom.

Raids and cattle theft had been a sporadic problem along the Mexican border for decades, but in 1915, revolutionaries began to target symbols of American oppression for destruction, including farms, irrigation systems, and railroad lines. Local law enforcement could not cope with the escalating lawlessness. The Texas governor dispatched the Texas Rangers to restore order and chase the revolutionaries back to the Mexican side of the line. (The unrest spanned the terms of three governors: Oscar Colquitt, James E. "Pa" Ferguson, and William Hobby.) As the violence grew worse, the legislature authorized the creation of special companies called Loyalty Rangers to police the border.

Unfortunately, these Rangers wrote a black chapter in the history of their organization. Not content to police the area, they engaged in heavy-handed bullying of the Tejano population and worse. It is estimated that as many as 5000 Hispanics were killed by the Rangers between 1914 and 1919. (About 400 white Texans were killed in the unrest on the border, and millions of dollars in property was destroyed.) Some shocking atrocities were perpetrated against civilians on both sides.

In 1918, Texas state representative José T. Canales of Brownsville launched an investigation into the conduct of the Texas Rangers during the border wars and filed nineteen charges of misconduct against the Rangers. The following year, the Texas legislature formed a joint House-Senate committee to look into Canales's charges. They heard testimony for two weeks.

As a result of the investigation, the Loyalty Rangers were abolished, and the Texas Rangers were reduced in force. Higher recruiting standards were put in place, and the pay of Rangers was increased to attract and retain higher-quality officers. Finally, procedures were implemented to better hear complaints from citizens about misconduct. These reforms helped the Rangers return to a position of respect during the 1920s and 1930s