The exodus of the Saints from Nauvoo into Iowa Territory commenced on February 4, 1846 when the first wagon ferried across the Mississippi River. The historic freeze-over of the Mississippi River occurred on February 24, 1846 that allowed a more expeditious evacuation of the heavy wagons and foot traffic. The Nauvoo exodus extended from February to September 1846. Families were spread over Iowa Territory, setting up refugee tent and wagon camps, such as at Mt. Pisgah and Garden Grove, and crude shelters at Council Bluffs and Winter Quarters. At these locations the Saints regrouped and labored to acquire the necessary supplies and equipment for continuation of their immigration outside of the United States boundaries and across the plains of Nebraska to an unknown final destination somewhere west in the Rocky Mountains.
Even before this exodus was in progress, issues had been escalating between the United States and Mexico over disputed Texas territory. In 1836, Texas proclaimed itself an independent republic. However, Mexico never recognized Texas independence, considering it a rebellious providence which would eventually be retaken as part of the Republic de Mexico. On July 4, 1845, Congress ratified a bill granting statehood, and Texas officially became the 28th State of the Union on December 29, 1845. This annexation of Texas caused Mexico to sever diplomatic relations with the United States. The territorial dispute between Texas and Mexico centered on the Texas claim of all land north of the Rio Grande, but Mexico recognized the Nueces River as the southern Texas boundary.
Hoping to avoid war, and knowing that Mexico was in dire financial straits from internal civil wars and in desperate need of cash, President James K. Polk sent John Slidell as a special emissary to Mexican governmental officials in Mexico City with an offer to: (1) absorb the $3 million ($75 million in today’s value) in damages owed to U.S. citizens from the Mexican War of Independence, and (2) purchase the disputed Rio Grande territory, Santa Fe Nuevo Mexico and Alta California for $25-30 million ($650-750 million in today’s value). Because of internal political instability and national honor, the Mexican government refused this offer.
President Polk had already ordered General Zachary Taylor to move his Army of Occupation (protection of Texas) to the Rio Grande where he built a makeshift Fort Texas (later named Fort Brown) opposite the Mexican city of Matamoros. On April 25, 1846, a 2000-man Mexican cavalry unit attacked a 63-man detachment of U.S. dragoons patrolling the disputed land between the Rio Grande and the Nueces River, killing 11 and capturing most of these mounted U.S. soldiers. General Taylor reported back to President Polk that this incident on American soil could be considered an act of war. President Polk announced to Congress that, “Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil. She has proclaimed that hostilities have commenced, and that the two nations are now at war.” After a short debate, the U.S. Congress declared war on Mexico on May 13, 1846 and Mexico reciprocated with its own declaration of war on May 23, 1846.
The U.S. War Department formed three main armies to wage this war with Mexico: (1) the Army of Occupation under General Zachary Taylor to proceed across the Rio Grande and south to Monterrey; (2) the Army of the Center under General John E. Wool to depart from San Antonio into northern Mexico, with Chihuahua as the initial objective that was later changed to Parras, and (3) the Army of the West under Colonel Stephen Watts Kearny (later promoted to Brigadier General) to recruit a battalion force of volunteers from among the Mormons in Iowa and proceed from Kearny’s headquarters at Fort Leavenworth, Kansas going overland to secure the provincial capital of Santa Fe, then across the Sonora desert to unite with U.S. naval and marine forces under Commodore Robert F. Stockton to secure San Diego and Alta California. In late 1846,
a plan was formulated in which General Winfield Scott, Commanding General of the U.S. Army, was to amass a fourth army initially deploying from New Orleans to conduct an amphibious landing at Vera Cruz, then proceed west to Mexico City. Congress authorized reinforcing the small number of the regular U.S. Army (about 8600 men) with 50,000 volunteers organized as militia units from the various States. For example, two mounted volunteer units, 1st Mounted Missouri Volunteers and the 2nd Mounted Missouri Volunteers, were organized under the command of Colonel Alexander Doniphan and Colonel Sterling Price, respectively. These cavalry and artillery units assembled at Fort Leavenworth as part of Kearny’s Army of the West. They traveled to Santa Fe from where Doniphan received orders to advance into Mexico and take Chihuahua and then join forces with Gen. Wool’s Army of the Center near Monterey. Price was to take command and garrison in Santa Fe to provide continued protection to the citizenry against marauding Apache and Navajo raiding parties.
Just before the exodus of the Saints out of Nauvoo, on January 26, 1846 Brigham Young sent correspondence with Jesse C. Little, acting as President over the New England and Middle States Mission, with instructions to petition for financial assistance from national leaders in Washington, D.C. On 21 May 1846, 8 days after the congressional declaration of war against Mexico, Little arrived in Washington, D.C. After initial visits with the vice-president and other federal officials, Thomas L. Kane provided Jesse C. Little with letters of introduction to influential governmental officials in Washington, D.C. Little sought the influential former postmaster general and cabinet member in the Jackson administration, Amos Kendall, who counseled with President Polk and Elder Little concerning the Mormon situation. Little was joined by Thomas L. Kane and together they lobbied for government assistance for the impoverished Mormon refugees. Thomas Kane, the son of a prominent federal judge, had become sympathetic to the Mormon plight and became a dedicated ally and advocate for the Mormons with the
federal government and U.S. Army throughout his life. Instead of accepting Brigham Young’s proposal of a series of federally financed fortifications across the West, built and maintained by the Saints, President Polk agreed to enlist a volunteer battalion of 500 Mormon men in Iowa to join Colonel Kearny’s Army of the West.