The 1850 Boundary Act
The Boundary Act of 1836 established the entire length of the Rio Grande as the southern and western boundary of the Republic of Texas, even though colonization was confined principally to the territory between the Nueces and the Sabine. When Texas entered the union, these territorial limits were retained, and the Treaty of Guadalupe Hidalgo confirmed the Rio Grande as the southern boundary between Texas and Mexico.
President Mirabeau B. Lamar and Governors George T. Wood and Peter H. Bell attempted to extend Texan control in the Santa Fe and New Mexico area. Their efforts failed: the Santa Fe Expedition was captured by Mexican forces in 1841 and post-annexation extension of Texan influence met with great opposition in the New Mexico territory.
By 1850, New Mexicans had ratified a proposed state constitution, one which defined boundaries well within territory claimed by Texas, Governor Bell convened the Texas Legislature to enforce the state's claim, President Millard Fillmore threatened to resist any such claim with military force, and a series of bills were offered in the Congress in an effort to resolve the problem. Senator Thomas Hart Benton of Missouri would have had Texas cede all land west of 102° longitude and north of the Red River, divide Texas into two states, and pay $15 million for the lost territory. Senator John Bell of Tennessee would have had Texas split into three states. Yet another proposal would have drawn a straight line from El Paso to the point where the 100th meridian meets the Red River, in exchange for an unspecified payment.
The bill proposed by Senator James A. Pearce of Maryland offered $10 million in 5% U.S. bonds in exchange for ceding to the national government 67 million acres of land north and west of a boundary beginning at the 100th meridian where it intersects the parallel of 36°30', then running west along that parallel to the 103d meridian, south to the 32d parallel, and from that point west to the Rio Grande. At least half of the $10 million payment would be dedicated to retiring the public debt of the Republic of Texas.
The Boundary Act also provided "That nothing herein contained shall be construed to impair or qualify anything contained in the 3rd article of the 2nd section of the "Joint Resolution for annexing Texas to the United States," approved March 1, 1845, either as regards the number of States that may hereafter be formed out of the State of Texas, or otherwise.
Texas voters accepted the proposal with a three to one majority, and Governor Bell signed the act on November 25, 1850.