By Donald S. Frazier
During the rapid expansion of the United States in the nineteenth century, establishing an exact western and southern boundary for the country plagued the nation and its neighbors alike. The original western border of the Mississippi River, established in 1783 at the conclusion of the American Revolution, stood for twenty years. In 1803, the Louisiana Purchase put the U.S. boundary back into question by doubling the size of the federal domain but describing its limits in only the vaguest language. Based on original French claims, the United States, under the leadership of Thomas Jefferson, attempted to press a claim on portions of Texas, but to no avail. A compromise with Spanish officials created a neutral ground between the two domains. Even so, illegal border incursions occurred on a regular basis, starting with Lewis and Clark's expedition to the Pacific from 1803 to 1806, which established a claim of joint tenancy with Great Britain over the Columbia River region - this despite a previous Spanish claim. The United States annexed Spanish West Florida in 1810 after U.S. settlers there staged an insurrection and declared their independence from Spain. Andrew Jackson's invasion of Florida (1817-1818) and several filibustering expeditions into Texas exacerbated the boundary question. Finally, in 1819, the ratification of the Adams-Onis Transcontinental Treaty clearly defined the frontiers of Spanish and U.S. lands and ended a decade and a half of bellicose posturing.
Upon achieving independence in 1821, Mexico's inheritance included this legacy of boundary disputes. When U.S. immigrants began to settle in Texas in the 1820s, the government in Mexico City quickly became aware of the potential threat looming on their northern and eastern border, with the possibility that these new citizens might in fact serve as clandestine agents of U.S. expansion. Andrew Jackson, his appetite for territorial acquisition well established, enlarged this image of U.S. territorial aggrandizement by repeatedly attempting to purchase Texas from Mexico. Failing this, many observers suspected him of sending agents, including his friend Sam Houston, into the region to agitate for Texas independence on the West Florida model. By 1836, Texan independence had changed the boundary of the United States and Mexico.
The ten-year existence of this sovereign state further complicated the disputed border. Mexico never recognized the independence of Texas and therefore claimed the 1819 borders as intact. The United States, as well as Great Britain and France, however, did approve of Texas's claim to nationhood. The question remained as to the precise western and southern borders of the nation. In 1836, Texas pressed a frontier claim south to the Rio Grande and west to its source in spite of the lack of historical precedent. This put into dispute the Trans-Nueces region, or the Seno Mexicano, long a part of the Mexican state of Tamaulipas, as well as most of Nuevo Mexico. In subsequent years, Texas legislatures claimed even more Mexican territory, eventually laying claim to the Californias. Starting in 1841, Texas attempted to press its claim to eastern New Mexico militarily, but without success.
Diplomacy would intervene to settle the issue, or so it appeared. An armistice between Texas and Mexico in 1844 hinted at recognition of Texas independence, but the boundaries remained at issue. Meanwhile, Lone Star agents worked for annexation to the United States, a goal sought by the vast majority of Texans. Their efforts, however, were themselves retarded by the vagueness of Texas borders as the issue aggravated fears of abolitionists that slavery would be extended across the continent.
In 1845, the United States had worked out its own reluctance regarding the expansion of slavery and intervened in the question of national boundaries once again by annexing Texas through a joint resolution of Congress. That same year, it settled its dispute with Great Britain over the Oregon country. When Gen. Zachary Taylor's army moved from U.S. territory to Corpus Christi, Texas, all observers realized that the issue of borders between the United States and Mexico would be resolved at the point of the bayonet. Indeed, by the end of the U.S.-Mexican War, not only had Texas been secured, but so had a large swath of territory including Alta California, Nuevo Mexico, and large portions of the Mexican states of Chihuahua and Sonora in a vast tract known simply as the Mexican Cession. Even with this enormous acquisition, many in the United States advocated the annexation of all of Mexico and grumbled at their government's failure to do so.
This latest adjustment of frontiers led to further conflict. The boundary commissioners of both nations could not agree on an exact starting point from which to begin their surveys. Eventually, officials settled this issue through negotiation and compromise. The territorial claims of Texas, however, were not as easily settled. Opposed by abolitionists and stunned by the creation of a territorial government in Santa Fe, New Mexico, by occupying U.S. forces, Texas politicians threatened war to bring back the "rebellious counties" it had organized, at least on paper, from eastern New Mexico. The rhetoric of President Zachary Taylor and Governor Peter H. Bell waxed hot, but the two sides never came to blows. Instead, politicians settled the issue peacefully as part of the Compromise of 1850.
Three years later, the Gadsden Purchase settled most of the remaining issues regarding the disputed border between the United States and Mexico. The need for a southern transcontinental railroad route and the inability of the United States to control Apache raids into Mexico led to a modification of the Treaty of Guadalupe Hidalgo. The resulting agreement, negotiated by James Gadsden and Antonio Lopez de Santa Anna, sold additional Mexican territory to the United States and established the borders as they exist to the present day. Surprisingly, the final arrangements were for the least amount of territory requested by the United States at the maximum price authorized by Gadsden's instructions.