Election of 1800
Rematch of the election of 1796, but with a different outcome as Republican Thomas Jefferson prevailed over incumbent president, John Adams by taking New York and parts of Pennsylvainia that had backed Adams and the Federalists four years earlier. Thomas Jefferson called the election of 1800 "as real a revolution in the principles of our government as that of 1776 was in its form." The election of 1800 marked the transition of power from Federalists to Republicans, and began a period of tearing down the Federalist style of government and building up a Republican framework.
Louisiana Purchase
Negotiated in April 1803, the Louisiana Purchase was one of the most important events in US history. It doubled the size of the nation, opening the west to exploration and settlement. With the Louisiana Purchase came the possibility of expansion and also the strife which would accompany the admission of new states from that region. Additionally, the Louisiana Purchase created a period during which the US could not detangle itself from foreign affairs, as its borders were increasingly changing and called into question.
XYZ Affair
In response to continued French aggression at sea, John Adams sent a diplomatic envoy to France to negotiate for peace in 1797, just after a coup d'etat in the directory. Charles de Talleyrand, the new French foreign minister, refused to meet with the US delegation, instead sending three anonymous agents, X, Y, and Z. The agents delivered the message that Talleyrand would not begin talks until he received $250,000 for himself, and France received a $12 million loan. This widely publicized (in America) attempt at extortion aroused public outrage among the American people, some of whom called for war.