When the Constitution was written in 1787, the United States was a narrow strip of states along the East Coast of North America. Within 70 years, it stretched from the Atlantic Ocean to the Pacific. That expansion was driven by ambition, purchase, and war — and at every step, it came at an enormous cost to the Native American peoples who had lived on that land for centuries.

The United States in 1787

When the Constitution was first written, the United States had 13 states on the East Coast. The country also claimed ownership of the land between those states and the Mississippi River. However, more than 600,000 Native Americans were still living on that claimed land — people whose tribes had been there for thousands of years and who did not accept that the United States owned it. This disagreement led to widespread conflicts and wars throughout the 1800s, as Native Americans were forced to defend their people, their culture, and their land.

The Louisiana Purchase (1803)

In 1803, the United States made one of the most consequential land deals in history, purchasing the Louisiana Territory A vast tract of land between the Mississippi River and the Rocky Mountains, purchased by the United States from France in 1803. The purchase roughly doubled the size of the country. from France. The Louisiana Territory encompassed a huge area of land stretching from the Mississippi River all the way to the Rocky Mountains. France agreed to sell because it needed money to fund the wars it was fighting in Europe.

The purchase dramatically expanded the size of the United States and opened up vast new territories for settlement. But it also accelerated conflicts with the Native American nations who lived there.

The Trail of Tears

As settlers pushed westward into the newly acquired territory, conflicts with Native Americans intensified. Between the 1830s and 1850s, the U.S. government forced people from five Native American nations in the southern United States to leave their ancestral homelands and relocate to land in the Louisiana Territory. The five nations forced to relocate were the Cherokee One of the five Native American nations forced to relocate westward by the U.S. government in the 1830s–1850s. , Muscogee, Seminole, Chickasaw, and Choctaw.

This forced relocation became known as the Trail of Tears The forced relocation of people from five Native American nations — the Cherokee, Muscogee, Seminole, Chickasaw, and Choctaw — from their homelands to territory in present-day Oklahoma during the 1830s–1850s. Thousands died from disease and starvation along the journey. — a name reflecting the immense suffering the journey caused. Thousands of people died from disease and starvation along the way. Throughout the remainder of the 1800s, westward expansion continued to displace Native American communities, with more and more tribes forced off their lands.

The Mexican-American War (1846–1848)

As the United States expanded, its ambitions brought it into direct conflict with its southern neighbor. In 1845, Texas became the 28th state to join the United States. Texas had been part of Mexico until 1836, when it fought for and won its independence, existing as its own country from 1836 to 1845. Mexico still claimed much of the land in the southwest between the Rocky Mountains and the Pacific Ocean, and also wanted Texas returned to Mexican territory.

In 1846, the United States went to war with Mexico over Texas and other southwestern lands Mexico controlled. This was the Mexican-American War A war fought between the United States and Mexico from 1846 to 1848, resulting in the U.S. gaining significant territory in the southwest, including what became California, Nevada, Utah, and parts of Arizona, Colorado, New Mexico, and Wyoming. . The United States won the war in 1848. Under the peace treaty that followed, Mexico accepted that Texas was part of the United States and agreed to sell its southwestern land claims to the U.S. The territory gained from Mexico later became the states of California, Nevada, and Utah, as well as parts of Arizona, Colorado, New Mexico, and Wyoming.

Reaching the Pacific

In 1850, California became the 31st state to join the United States — and the first state to border the Pacific Ocean. By 1860, there were 33 states in the Union. The country now stretched from the Atlantic Ocean on the East Coast to the Pacific Ocean on the West Coast, and claimed all the land between Canada and Mexico that makes up what are today the first 48 states.

But expansion came at a cost beyond war and displacement. As settlers from both the North and the South moved westward, they brought with them a conflict that had been simmering since the founding of the country: the question of slavery. Whether slavery would be legal in the new states and territories became the defining political battle of the mid-1800s — and ultimately the spark that ignited the Civil War.

Wrapping Up

The story of westward expansion is one of extraordinary ambition and equally extraordinary human cost. The Louisiana Purchase doubled the size of the country in a single transaction. The Trail of Tears displaced and devastated five Native American nations. The Mexican-American War added vast new territory across the southwest. And by 1860, the United States spanned an entire continent — but was on the verge of tearing itself apart over the unresolved question of slavery. The next subchapter picks up exactly there.