New York journalist John O'Sullivan writes an essay urging the United States to annex the Republic of Texas because it was America's "Manifest Destiny. . .to overspread the continent allotted by Providence for the free development of our yearly multiplying millions."

At the year's end, Mexico severs diplomatic relations with the United States following the decision by the United States to annex Texas.  President Polk sends General Zachary Taylor to the Mexican border.


In March John C. Frémont begins his third expedition into the West, during which he will proclaim California an independent republic. The “Bear Flag Revolt” ends quickly when American naval forces arrive in Monterey and claim California for the United States.

In May war breaks out between Mexico and the United States when a Mexican force crosses the Rio Grande River and attacks an American cavalry patrol.

The United States acquires Oregon in June when Britain agrees to the establishment of this Territory’s northern border at the 49th parallel.

Following the death of Joseph Smith by a mob in Carthage, Illinois in 1844 and subsequent violence directed toward Mormon followers, Brigham Young leaves Illinois to establish a new settlement in the West.


In January Mexican authorities surrender control of California.

General Zachary Taylor is victorious at the Battle of Buena Vista in February, and the Mexican army is forced to retreat. General Winfield Scott and his forces land at and occupy the town of Veracruz the following month.

In July Brigham Young arrives in the Great Salt Lake Valley in Utah with an advance party.


In January James Marshall discovers gold in California’s American River. When President Polk announces the news in December, the California gold rush begins.

In February the Treaty of Guadalupe Hidalgo between the United States and Mexico is signed, thereby ending the Mexican War. It stipulates that Mexico transfer much of the present-day American Southwest for $15 million.


Francis Parkman’s The Oregon Trail is published.

More than 80,000 “Forty-niners” arrive in California by the year’s end, nearly tripling the Territory’s population. After failing prospecting in California, Domingo Ghirardelli opens a general store in Stockton and later one in San Francisco, where he begins selling chocolate.


California enters the Union as a free state following the passage of the Compromise of 1850.

President Fillmore names Brigham Young the territorial governor of Utah.

Bayard Taylor’s Eldorado, or Adventures in the Path of Empire is published.

New Mexico becomes a United States Territory. French priest Jean Baptiste Lamy is made the bishop of the diocese of Santa Fe.


The United States signs the Fort Laramie Treaty with representatives of various Plains tribes. The treaty calls for peace and divides the region into designated tracts for different native groups. In return, the United States agrees to protect them and to grant each tribe $50,000 annually for the next fifty years.


William Fargo and Henry Wells establish Wells, Fargo and Company to provide mail service and transportation to California.

Washington becomes a United States Territory.


James Gadsden, the U.S. minister to Mexico, negotiates the purchase of additional land in the Southwest for $10 million to be used for a proposed transcontinental railroad.

William Walker leads a “filibustering” expedition to Baja California and proclaims it the Republic of Lower California. Mexican forces drive him back over the border, and the plan is scuttled.


The Kansas-Nebraska Act is passed, overturning the Missouri Compromise of 1820 and permitting each Territory to choose whether it will permit slavery.


Abolitionist John Brown and his followers engage in a series of deadly skirmishes with pro-slavery forces in Kansas.


Explorer John C. Frémont is nominated as the first Republican candidate for the presidency, but loses to James Buchanan.

Settler Olive Oatman is freed after five years of captivity with the Apache.


Kansas citizens reject the pro-slavery Lecompton Constitution.

After complaints regarding the Mormon practice of polygamy, President Buchanan orders troops to Utah to ensure that federal laws are being obeyed. The “Mormon War” ends a year later.


Gold is discovered in Colorado, and the Pikes Peak gold rush begins.


Oregon enters the Union as a free state.

Silver is discovered in Nevada at the Comstock Lode.

The Atchison, Topeka, and Santa Fe Railroad is chartered.

Albert Bierstadt accompanies a surveying expedition led by General Frederick Lander to Wyoming and begins his career as a painter of the West.


The Pony Express is established, providing regular mail service from St. Louis to San Francisco. The service ends a year later, eclipsed by a transcontinental telegraph line.

President Buchanan vetoes a proposed Homestead Bill that will provide federal land grants to Western settlers. Later that fall Abraham Lincoln is elected president.

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