Why did the election of 1800 mark an important turning point in American political history?

 Federalists and Democratic-Republicans continued to fight throughout the first years of the new nation, especially during the presidency of John Adams (1797-1801). In 1798, Adams signed the Alien and Sedition Acts, which were directed against opponents of his government. Three of these four acts were aimed at recent immigrants to the U.S. The fourth, however, the Sedition Act, outlawed criticism of government policies and the president, and was used to suppress newspapers that opposed Adams's government. Democratic-Republicans were outraged by this law. Southern Democratic-Republicans wrote the Kentucky and Virginia Resolves, which declared the Sedition Act a violation of Americans' freedoms, and vowed opposition to the Act. According to these Resolves, individual states could nullify laws that they considered contrary to the Constitution. This theory of nullification, and that the states could defy laws passed by Congress, would later be used by white Southerners to defend slavery.

In 1800 Thomas Jefferson campaigned against John Adams for the presidency. In one of the most heated and closest elections in American history, Jefferson defeated the incumbent. Jefferson, who had authored the Declaration of Independence, stated that "The Revolution of 1800 was fully as important as the Revolution of 1776." He considered his election as president a revolution because he believed that he had saved the republic from Federalists' determination to deprive citizens of their liberties. When Jefferson was inaugurated in March 1801, and power was transferred peacefully from the Federalist Party to the Democratic-Republicans, an important milestone in American history had been reached. Americans' bold, even risky effort to create a workable new form of government under the Constitution finally seemed likely to endure. The revolution against Great Britain had now produced not only American independence, but a stable form of government, one capable of meeting the new nation's challenges and accommodating a wide diversity of political views.