Revolution toppled Spanish rule and established Mexico as an independent republic. The Mexican republic is rich in resources and a target of expansionists.
Jedediah Smith, a mountain man, crosses the Great Basin and the Sierra Nevada to reach California. This route later became known as the California trail and linked the USA with the Pacific.
Marcus and Narcissa Whitman blaze the Oregon Trail to found an Indian mission and a way station for later settlers.
An official government expedition is led by John Frémont that brings publicity to the Far West and eventually draws thousands of settlers there.
John L. O'Sullivan writes an influential editorial in favor of expansion that coins the name Manifest Destiny.
The Donner party gets lost and is trapped by the snow in the Sierra Nevada. The Survivors resort to cannibalism showing the hardships of westward expansion.
Brigham Young leads the Mormons across the Great Plains and Rockies to establish the colony of New Zion on the eastern shore of the Great Salt Lake. New Zion eventually becomes Utah.
Th Treaty of Fort Laramie binds the Indians to territories away from major trails. This Treaty leads to future conflict between settlers and Indians.