In the predawn fog of September 23, 1810, about 50 men, led by Revolutionary War veteran Philemon Thomas, walked in the open gate of Fort San Carlos in Baton Rouge. An additional 25 men on horseback rode through a gap in the fort’s wall. Spanish soldiers discharged a handful of muskets before Thomas’ men let go a single volley that killed or wounded five Spaniards. The remaining soldados surrendered or fled.

Revolutions come in all shapes and sizes, but the West Florida Rebellion holds the record as the shortest. In less than one minute it was over, setting in motion a chain of events that would transform the United States into a continental and, eventually, world power.

The nation’s expansion had begun seven years earlier, when President Thomas Jefferson purchased the Louisiana Territory from France. But Spain, which had ceded the territory to Napoleon, maintained that it did not include the area known as West Florida, which stretched from the Perdido River across southern Alabama, Mississippi and Louisiana to the Mississippi River. For its part, the United States believed West Florida was its own, but rather than risk confrontation and war, Jefferson and his successor James Madison allowed Spain to administer it until an opportunity arose.

Things were peaceful until 1808, when Spain appointed Col. Charles Delassus as governor. The inefficiency and corruption of officials under him threatened the prosperity of American colonists in West Florida, who presented demands for political reform. Delassus pretended to go along, while secretly plotting to arrest the ringleaders.

Learning of Delassus’ duplicity, the Americanos struck first. After capturing Fort San Carlos, they declared the Republic of West Florida, replacing the Spanish flag with their banner—a white star on a field of blue. Some derided what one U.S. newspaper editor called “the little mimick Revolution,” but President Madison knew that his strategy of passive expansionism had evicted Spain at no expense to the United States.

On December 10, 1810, the Republic of West Florida’s lone star came down and the Stars and Stripes took its place. For the first time, the United States had acquired significant territory from another sovereignty without war or compensation.

It didn’t take long for other territories to follow West Florida’s example. In 1835-36, Texas rose in revolt against Mexico, fighting under West Florida’s lone star flag and voluntarily submitting to U.S. annexation in 1845. (The five-point star had emerged as a symbol of enlightenment and defiance against tyranny—and would remain a motif for the flag of the Texas Republic.)

A year later at Sonoma, a small band of American and Mexican settlers declared the California Republic. The subsequent revolt against local authorities lasted 26 days before the United States took over. In the ensuing war with Mexico, the United States acquired all of California and most or all of Colorado, Nevada, New Mexico, Arizona, Wyoming, Utah and Oklahoma.

While much has been written about the U.S.-Mexican War, the event that started it all, the 1810 revolution, has largely been viewed as a footnote. As a historian, it became clear to me that there was more at work here than a small band of unruly, land-hungry American colonists. West Florida became the template for Manifest Destiny—a near-perfect embodiment of the men and forces that would propel Americans across their continent.