As Americans began to move further and further to the West, we encountered territorial conflict. In 1845, the United States annexed the Repubic of Texas prompting military action. The Mexican War lasted from 1846 to 1848, and led to the extension of our borders to the Pacific Ocean.
Kentucky was required to furnish four regiments of volunteers following the declaration of war against Mexico The required number of soldiers was 2,400 men, but in Kentucky, nearly 15,000 answered the call. Four of the most important U. S. commanders were native Kentuckians: Major General Zachary Taylor, Major John C. Breckinridge, Lieutenant Colonel Thomas L. Crittenden, Lieutenant Colonel Henry Clay, Jr., who lost his life in the battle of Buena Vista and Captain Cassius Clay. In all, over 600 Kentucky soldiers became casualties during the two year conflict.
Boone County's own John P. Gaines volunteered and served as a Major and General Winfield Scott’s aide-de-camp during the conflict. Edward Riley Sprigg Canby who was chief of staff of Riley's Brigade, also received promotions of major and lieutenant colonel for his actions during many battles of the Mexican War.