In October 1821, Long was defeated by Spanish troops, captured and sent to Mexico City where he was killed by a guard.

In particular, the Mexican War of Independence made it difficult for Spain to adequately protect its more remote territories such as Texas.

Lured by the promise of free land and potential wealth, many men from the United States joined expeditions to try to take Texas from Spain.

The expeditions were largely planned in New Orleans and variously wished to establish an independent republic in Texas or assist the revolutionaries fighting within Mexico.

In early 1819, Spain and the United States signed the Adams–Onís Treaty, which established the boundary of the Louisiana Purchase at the Sabine River.

"[1] By the end of June, Long had received pledges for over $500,000, and about 200 men, including James Bowie and Ben Milam, had gathered for the expedition.

By July 16, the Spanish Consul in New Orleans had warned the viceroy in Mexico City that "I am fully persuaded that the present is the most serious expedition that has threatened the Kingdom".

Fifty men attempted to join him from the United States, but they were arrested by American authorities as they tried to cross into Texas.

He later broke with Milam, and the expedition led an uncertain existence until September 19, 1821, when Long and 52 men marched inland to capture Presidio La Bahía.

The town fell easily on October 4, but four days later Long was forced to surrender by Spanish troops under the command of Lieutenant Colonel Ignacio Pérez.

He was taken prisoner and sent to Mexico City, where about six months later he was shot and killed by a guard — reportedly bribed to do so by José Félix Trespalacios.