America was still mourning the death of George Washington as the new century dawned in 1800.

Washington died in December 1799, casting a shadow over the celebratory moment for the young republic. His passing marked the end of an era and forced Americans to confront the reality of a nation moving forward without its most unifying figure.

Yet the nation was pressing ahead. In 1800, the federal government moved to its new capital, Washington, D.C., after earlier stints in New York and Philadelphia. On Nov. 1, 1800, President John Adams moved into the unfinished Executive Mansion. The building would be known for years as the President’s House before eventually becoming the White House.

The nation’s second census counted more than 5.3 million people in 1800, about half the population of Great Britain (England, Scotland and Wales). The figure reflected rapid growth but also dark realities: About 17% of the U.S. population, nearly 900,000 people, were enslaved.

There were 16 states in 1800, but the size of the nation would soon expand dramatically. Ohio entered the Union as the 17th state in 1803 as westward migration continued. That same year, the Louisiana Purchase would double the nation’s size, opening vast new lands to exploration and settlement. Meriwether Lewis and William Clark would lead an expedition across the continent, venturing into largely uncharted territory and reaching the Pacific Ocean.

New institutions also took root during this decade. The U.S. Military Academy at West Point and the Library of Congress were established, reflecting a growing commitment to national defense and intellectual development. Meanwhile, tensions with Great Britain and France simmered, and for the first time, the United States would project military power overseas in response to piracy along the Barbary Coast.

The first decade of the 19th century was a period of transition, testing and growth. Here are some of the events, people and milestones that made headlines.

The election of 1800 marked one of the most consequential political tests in American history. During the 1790s, partisan divisions between Federalists and Democratic-Republicans had deepened to the point that some observers feared the young republic might fracture.

The presidential election pitted incumbent President John Adams, leader of the Federalist Party, against Democratic-Republican Thomas Jefferson and his running mate, Aaron Burr. The campaign was bitter and personal, fought largely through partisan newspapers that published attacks, accusations and warnings about the dangers posed by the opposing side.

When the electoral votes were counted, Jefferson and Burr each received 73 votes, while Adams received 65. Because electors did not cast separate ballots for president and vice president, the tie between Jefferson and Burr created a constitutional crisis that the framers had not anticipated.

The Federalist-controlled House of Representatives was tasked with resolving the deadlock. For days, the House remained divided, voting repeatedly without reaching a decision. Finally, after 36 ballots and intense political maneuvering, Jefferson was elected president on Feb. 17, 1801, with Burr becoming his vice president.

The peaceful transfer of power between rival political parties was a landmark moment. Years later, Jefferson reflected on its significance in a letter to Judge Spencer Roane. The “revolution of 1800 … was as real a revolution in the principles of our government as that of [17]76. was in it's form; not effected indeed by the sword, as that, but by the rational and peaceable instrument of reform, the suffrage of the people.”

The crisis exposed flaws in the electoral system, leading to the ratification of the 12th Amendment in 1804, which required electors to cast separate votes for president and vice president. Jefferson won reelection that same year in a decisive victory, though he replaced Burr on the ticket.

Aaron Burr remained a central and controversial figure. Aware he was going to be replaced on the reelection ticket, he sought to revive his political fortunes by running for governor of New York in 1804. After his defeat, Burr blamed Alexander Hamilton, a longtime political rival, for undermining his campaign.

Reports that Hamilton had made disparaging remarks about Burr circulated in the press, prompting Burr to demand an explanation. When Hamilton refused to offer a full retraction, Burr challenged him to a duel — an illegal but still practiced method of settling disputes among gentlemen of the era.

The two men met on July 11, 1804, in Weehawken, N.J. The duel was brief but devastating. Hamilton’s shot missed, while Burr’s struck Hamilton in the abdomen. Hamilton died the following day, sending shock waves through the nation.

Although Burr was charged with murder in both New York and New Jersey, he avoided trial and completed his term as vice president. His political career, however, was effectively over.

In 1807, Burr faced even more serious charges when he was tried for treason, accused of conspiring to create an independent nation in the Western territories. The trial, presided over by Chief Justice John Marshall, ended in acquittal due to lack of evidence. Despite the verdict, Burr’s reputation never recovered, and he spent much of the rest of his life in relative obscurity.

Thomas Jefferson’s presidency was defined in large part by the Louisiana Purchase.

The Louisiana territory had been controlled by Spain before being transferred back to France in 1800 through a secret agreement. Jefferson, wary of French ambitions in North America, wanted to secure American access to the Mississippi River and the port of New Orleans, both vital to trade.

French leader Napoleon Bonaparte, facing mounting challenges in Europe and the Caribbean, reconsidered France’s position in North America. In 1803, he offered to sell the entire Louisiana territory to the United States.

The deal, finalized for $15 million, transferred approximately 828,000 square miles of land to the United States. Ratified by the Senate later that year, the purchase nearly doubled the nation’s size at a cost of about 4 cents per acre.

The acquisition raised constitutional questions, as Jefferson was unsure whether the federal government had the authority to purchase foreign land. Ultimately, he moved forward, recognizing the strategic and economic importance of the opportunity.

The Louisiana Purchase opened the door to westward expansion, setting in motion migrations, economic development and conflicts that would shape the nation for decades.

To better understand the newly acquired territory, Jefferson commissioned an expedition that would become one of the most famous journeys in American history.

Meriwether Lewis was selected to lead the expedition and chose William Clark as his co-leader. Together, they organized the Corps of Discovery, a group of soldiers, frontiersmen and interpreters tasked with exploring the Western lands and finding a potential water route to the Pacific Ocean.

Lewis departed Pittsburgh in 1803, traveling down the Ohio River before joining Clark near present-day St. Louis. On May 14, 1804, the expedition began its journey up the Missouri River.

The group built a fort near friendly Native American tribes, where they spent the winter of 1804-05. While at Fort Mandan, they recruited Toussaint Charbonneau as an interpreter. His pregnant Shoshone wife, Sacagawea, proved invaluable as a guide and cultural intermediary and would find a lasting place in American history.

In the spring of 1805, the expedition split, with some members returning east carrying scientific specimens and reports. The remaining party continued westward, navigating difficult terrain and crossing the Rocky Mountains under harsh conditions.

Later that year, they reached the Columbia River and eventually the Pacific Ocean. Clark recorded the milestone in his journal: “Ocian in view! O! the joy.”

After building Fort Clatsop and wintering there, the expedition began its return journey in 1806, arriving in St. Louis in September. The nearly 8,000-mile expedition provided detailed maps, scientific observations and valuable knowledge about the West, strengthening U.S. claims to the region.

American commerce faced significant challenges during this decade, both from overseas conflicts and shifting domestic policies.

For years, the United States had paid tribute to the Barbary States of North Africa to prevent attacks on American shipping. In 1801, Tripoli declared war on the United States, citing unpaid tribute.

President Jefferson responded by sending naval forces and Marines to the Mediterranean. The conflict, known as the First Barbary War, marked the first time the United States engaged in sustained military operations overseas. After several years of fighting, including a daring assault on the city of Derna, the war ended in 1805 with a negotiated settlement.

While the conflict boosted national pride, American shipping continued to face threats from European powers engaged in the Napoleonic Wars. Both Britain and France interfered with neutral trade, but British impressment of American sailors became a particularly contentious issue.

In an effort to avoid war, Congress passed the Embargo Act of 1807, halting U.S. exports and limiting imports. The policy was intended to pressure Britain and France economically, but instead it severely damaged the American economy, particularly in port cities.

Recognizing its failure, Congress replaced the embargo with the Non-Intercourse Act in 1809, allowing trade with all nations except Britain and France. The measure eased some economic pressure but did little to resolve underlying tensions.

The early 19th century also saw the Supreme Court assert its role in the federal system.

In 1801, President John Adams appointed John Marshall as chief justice. Marshall would serve for 34 years, the longest tenure in the court’s history, and would play a central role in shaping its authority.

His most significant contribution came with the 1803 case Marbury v. Madison. The case arose after William Marbury, appointed as a justice of the peace in the final days of the Adams administration, did not receive his commission from Secretary of State James Madison.

When Marbury petitioned the Supreme Court, Marshall faced a delicate situation. In his ruling, he declared that while Marbury had a right to his commission, the law granting the court authority to enforce it was unconstitutional.

In doing so, the court established the principle of judicial review — the power to declare laws passed by Congress unconstitutional. “A Law repugnant to the Constitution is void,” Marshall wrote, setting a precedent that remains fundamental to American law.

During this decade, the United States took steps to end its participation in the international slave trade.

A bill to prohibit the importation of enslaved people was introduced in Congress in 1805. President Jefferson publicly supported the effort in his 1806 message to Congress.

The legislation was passed and signed into law on March 2, 1807. Under the Constitution, however, Congress could not ban the importation of enslaved people before 1808, so the law took effect Jan. 1 of that year.

While the measure ended the legal trans-Atlantic slave trade, it did not end slavery itself, and illegal smuggling of enslaved people continued for years.

The political landscape continued to evolve as the influence of the founding generation began to shift.

By 1803, three of the four Alien and Sedition Acts had expired. Originally passed in 1798, the laws had granted the federal government broad authority to detain or deport noncitizens and restrict criticism of the government. The fourth, the Alien Enemies Act of 1798, remains in effect today and was invoked in 2025 by the Trump administration.

After serving two terms, Jefferson chose not to run for reelection, reinforcing the precedent of limited presidential tenure. His secretary of state, James Madison, was elected president in 1808.

Madison would soon face escalating tensions with Great Britain, leading the nation into the War of 1812 and ushering in a new phase of American political and military development.

As the federal government settled into Washington, social customs and traditions began to take shape.

President John Adams and first lady Abigail Adams hosted one of the earliest New Year’s Day receptions at the President’s House in 1801, beginning a tradition that would continue for more than a century.

Dolley Madison emerged as one of the most influential social figures in the capital. During Jefferson’s presidency, she frequently served as hostess at official events, since the president’s wife had died in 1782.

When James Madison became president in 1809, Dolley Madison continued in that role as first lady, becoming one of the most popular public figures of her time.

Cultural and educational life expanded alongside the nation’s political and geographic growth.

Children in the early 1800s likely learned their letters from “The New England Primer,” reprinted in 1803. More than 6 million copies were printed between 1681 and 1830.

Noah Webster’s “A Compendious Dictionary of the English Language,” published in 1806, represented an important step toward standardizing American English.

Mercy Otis Warren, the wife of Revolutionary War Maj. Gen. James Warren, published her three-volume “History of the Rise, Progress and Termination of the American Revolution in 1805,” establishing herself as one of the first prominent female historians in the United States.

Washington Irving’s “A History of New York,” published in 1809 under the pseudonym Diedrich Knickerbocker, offered a satirical take on the city’s past and contributed to its cultural identity.

In the visual arts, Charles Willson Peale founded the Pennsylvania Academy of the Fine Arts in 1805, creating the nation’s first major art museum and school.

The early republic invested in institutions that would shape its future.

In 1800, Congress approved $5,000 to establish a library for its use in the new capital, creating the Library of Congress. After British forces burned Washington in 1814, Thomas Jefferson sold his personal collection of 6,487 books to help rebuild the library.

The U.S. Military Academy at West Point was formally established on July 4, 1802. Originally a strategic fort during the Revolutionary War, it became the nation’s premier military training institution, producing generations of military leaders.

Innovation played a growing role in the nation’s economic development.

Éleuthère Irénée du Pont, a French immigrant, founded a gunpowder manufacturing operation near Wilmington, Del., in 1802. The enterprise would grow into one of the nation’s most important industrial companies.

In transportation, Robert Fulton’s steamboat Clermont made its successful voyage in 1807, traveling from New York City to Albany in about 32 hours. The achievement demonstrated the viability of steam-powered navigation and helped revolutionize trade and transportation.

In 1809, Mary Dixon Kies became the first woman to receive a U.S. patent in her own name, for a method of weaving straw with silk. Her innovation supported the growing New England hat industry and marked an important milestone for women in American innovation.

The decade from 1800 to 1809 was formative for the United States. The nation expanded geographically, strengthened its political institutions and began to assert itself on the global stage.

At the same time, unresolved tensions persisted. Conflicts with Britain and France continued to disrupt trade and challenge American sovereignty. By the end of the decade, the young republic — less than 30 years removed from independence — was moving steadily toward another war with Great Britain.

The foundations laid during these years would shape the nation’s future as America continued its journey from fragile republic to continental power.