U.S. Expansion

The Oregon Trail is a 2,200-mile (3,500 km) historic east–west large-wheeled wagon route and emigrant trail that connected the Missouri River to valleys in Oregon.
The eastern part of the Oregon Trail spanned part of the future state of Kansas and nearly all of what are now the states of Nebraska and Wyoming.

This was a treaty for the 49th parallel border between the United States and Canada

The treaty established the boundary of U.S. territory and claims through the Rocky Mountains and west to the Pacific Ocean, in exchange for the U.S. paying residents' claims against the Spanish government up to a total of $5,000,000 and relinquishing the US claims on parts of Spanish Texas west of the Sabine River and other Spanish areas, under the terms of the Louisiana Purchase.
Madrid decided to cede the territory to the United States through the Adams–Onís Treaty in exchange for settling the boundary dispute along the Sabine River in Spanish Texas.

Following a 13-day siege, Mexican troops under President General Antonio López de Santa Anna launched an assault on the Alamo Mission near San Antonio de Béxar (modern-day San Antonio, Texas, United States), killing all of the Texan defenders.
The news sparked both a strong rush to join the Texan army and a panic, known as "The Runaway Scrape", in which the Texan army, most settlers, and the new Republic of Texas government fled from the advancing Mexican Army.

The Senate's minority Democrats narrowly passed a compromise version of the House bill, with critical support from several southern Whigs, designed to provide the incoming President-elect Polk the option to effect immediate annexation of Texas or open new talks to revise the annexation terms of the House amended bill.

Rescuers from California attempted to reach the emigrants, but the first relief party did not arrive until the middle of February 1847, almost four months after the wagon train became trapped.
The journey west usually took between four and six months, but the Donner Party was slowed by following a new route called Hastings Cutoff, which crossed Utah's Wasatch Mountains and Great Salt Lake Desert.

American forces quickly occupied Santa Fe de Nuevo México and Alta California Territory, then invaded parts of Northeastern Mexico and Northwest Mexico; meanwhile, the Pacific Squadron conducted a blockade, and took control of several garrisons on the Pacific coast farther south in Baja California Territory.
The Treaty of Guadalupe Hidalgo ended and specified the major consequence of the war: the forced Mexican Cession of the territories of Alta California and Santa Fe de Nuevo México to the United States in exchange for $15 million.

The Treaty of 1818 set the boundary between the United States and British North America along the 49th parallel of north latitude from Minnesota to the "Stony Mountains"(now known as the Rocky Mountains).
Polk's offer to settle the boundary at the 49th parallel north, Democratic expansionists militantly called for the annexation of the entire region up to Parallel 54°40′ north, the southern limit of Russian America as established by parallel treaties between the Russian Empire and the United States (1824) and Britain (1825).

The Mexican Cession of 1848 is a historical name in the United States for the region of the modern day southwestern United States that Mexico ceded to the U.S. in the Treaty of Guadalupe Hidalgo in 1848, but had not been part of the areas east of the Rio Grande which had been claimed by the Republic, though the Texas annexation resolution two years earlier had not specified Texas's southern and western boundary.
Considering the seizures, including all of Texas, Mexico lost 55% of its pre-1836 territory in the Treaty of Guadalupe Hidalgo.[3] For only fifteen years from 1821 (when Mexican independence was secured) and the Texan Revolt in 1836, the Mexican Cession (excluding Texas) formed approximately 42% of the country of Mexico; prior to that, it had been a part of the Spanish colony of New Spain for some three centuries.

The administration of 14th President Franklin Pierce, strongly influenced by Secretary of War Jefferson Davis, (later President of the southern seceding Confederate States) saw an opportunity to acquire land for the railroad, as well as to acquire significant other territory from northern Mexico. In the end, territory for the railroad was purchased for $10 million ($260 million today), but Mexico balked at any large-scale sale of territory. In the United States, the debate over the treaty became involved in the sectional dispute over slavery, ending progress before the American Civil War in the planning or construction of a transcontinental railroad.
The Gadsden Purchase (known as Venta de La Mesilla or Sale of La Mesilla, in Mexico) is a 29,640-square-mile (76,800 km2) region of present-day southern Arizona and southwestern New Mexico that was purchased by the United States in a treaty signed on December 30, 1853 by James Gadsden who was the American ambassador to Mexico at that time.