The Yuma War was the name given to a series of United States military operations conducted in Southern California and what is today southwestern Arizona from 1850 to 1853. The Quechan (also known as Yuma) were the primary opponent of the United States Army, though engagements were fought between the Americans and other native groups in the region.

After the Mexican Cession, American settlers headed west over the Colorado River to take part in the California gold rush, many of whom crossed over Quechan lands. Seeing the opportunity, the Quechans established a ferry business near the junction of the Gila and the Colorado Rivers to transport American settlers on their way to California, drawing ire from white American ferry businesses operating on the Colorado River.

In early 1850, California outlaw John Joel Glanton and his gang of twelve men partnered with Jaeger's Ferry by sabotaging Quechan ferry operations and destroying their ferry. They then robbed and murdered both Americans, Mexicans, and natives as they traveled around and across the river. The Glanton gang also mugged the local Quechan chief and harassed the local Quechan.

In response, a Quechan war party retaliated by attacking Glanton's gang, killing nine. This act sparked the beginning of the Yuma War as news of the retaliation spread to California, provoking US military action.

California responded with the Gila Expedition, raising a militia of 142 men who were paid $6 a day to fight the Yuma as opposed to panning gold. Setting off on April 16, the Gila Expedition entered what is today Arizona only to be besieged and defeated in September after a series of skirmishes. The expedition was a failure and due to the inflated prices caused by the gold rush, cost the State of California 113,000 dollars, a sum which nearly bankrupted the state.^{[citation needed]}

Following the failure of the California Militia against the Quechan people (Yuma Indians), in the Gila Expedition, the U. S. Army sent the Yuma Expedition under Captain Samuel P. Heintzelman, to establish a post at Yuma Crossing of the Colorado River in the vicinity where it met the Gila River in the Lower Colorado River Valley region of California. He was to protect travelers on the overland route from the east to California and to quell any hostilities by the Quechan people (Yuma Indians).

After reconnoitering his route, Heintzelman marched out of San Diego on 3 October 1850 with three companies of the 2nd Infantry Regiment with another infantry company establishing a depot at Vallecitos. He then sent a small party in advance digging wells in the desert between Vallecitos and the Colorado River. He reached Vallecitos on November 3 and the Yuma Crossing on November 27, a third company arriving a few days later. Camp Yuma was established with the tents protected from sun and wind by brush and reed fences and arbors. A garden and vineyard were started near the river. The Quechan living in the vicinity of the camp were quiet and friendly.

In February 1851, Heintzelman again met with some Quechan leaders along the Colorado. Presenting them with tobacco, food and other gifts, the Quechan were very pleased and expressed their fear of the Maricopa who lived along the Gila River and were raiding Quechan villages. Heintzelman attempted to secure a peace between the Quechan and Maricopa.