In 1849, after the region was ceded to the United States at the end of the Mexican–American War, an American pioneer named Lucien B. Maxwell moved to the area, married Beaubien's daughter, and became a part owner and manager of the vast land grant.

Over the following decades, many more pioneer families arrived in the area, which was conveniently situated along branches of the Santa Fe Trail.

Their arrival and purchase of the land immediately spurred controversy among the people already living in the area, and animosity quickly developed between the two sides.

Many of these settlers were white, Spanish, and Native American people who believed that the land was in the public domain or felt that they had been given Maxwell's unwritten permission to live on the grant.

[3] The event that triggered much of the war, was the murder of Reverend Franklin J. Tolby, a staunch ally of the settlers and squatters opposing the Maxwell Land Grant Company.

However, they soon shifted sides when Griego and his family were faced with charges of killing three cavalry men in an altercation in a card game, and also implicated in the suspected murder of another soldier on June 1.

[4][5] With his family's reputation of violence and betrayal, Vega was an easy prime suspect and soon the townspeople, led by notorious gunfighter and advocate of the settlers Robert Clay Allison, formed a mob to hunt him down.

[7] Company gang members retaliated by conducting night-time raids on the settlers, destroying their property as well as murdering those who fought back.

The Maxwell Land Grant and Railway Company was also allied with the powerful Santa Fe Ring, a group of influential lawyers and politicians who controlled many Western states.

The Dutch owners also faced financial instability and were sued by the United States government in the early 1880s for making claims on land within the public domain in Colorado.