William H. Bissell, a partially paralyzed war hero who had served in the Mexican War, was inaugurated as the first Republican governor of Illinois. (By Matthew Pinsker)

In the first ruling in Philadelphia following passage of the new federal Fugitive Slave Act, Justice Robert Cooper Grier freed a black man who had been claimed as a runaway slave by Mary Saunder. The verdict sparked celebrations outside the courthouse and results in two arrests of local blacks. (By Matthew Pinsker)

Iowa became the nation's 29th state, joining the Union as a free state. (By Matthew Pinsker)

After Mexican troops fire upon U.S. forces attempting to blockade a Mexican border town, Gen. Zachary Taylor reports to Congress that "hostilities may now be considered as commenced." (By Matthew Pinsker)

Gen. Taylor's forces won the second engagement of the Mexican War, decisively defeating a much larger contingent of Mexican troops at Resaca de la Palma.

Mexican troops attack Fort Texas, a U.S. outpost established by Gen. Zachary Taylor's men in the disputed Texas border area. Taylor and most of the men who had built the fort had previously redeployed further north along the Rio Grande River, leaving the small outpost vulnerable. (By Matthew Pinsker)

General Zachary Taylor's troops crossed the Rio Grande and occupied the Mexican border town of Matamoros. (By Matthew Pinsker)

About this date and throughout the spring of 1846, over 12,000 Mormons began a massive migration from Nauvoo, Illinois to Council Bluffs, Iowa.

Congressman Robert C. Winthrop famously invoked "the right of our manifest destiny to spread over this whole continent" in a debate preceding a House vote to end the joint Anglo-American occupation of the Oregon Territory. (By Matthew Pinsker)