McConnell's Historical Atlas from 1919 provides an color-coded overview of the Louisiana Purchase of 1803, as well as subsequent international actions. To view this resource in full, visit: https://www.loc.gov/item/2009581130/.

The Louisiana Purchase of 1803 is one of American history's most celebrated accomplishments: a real estate deal that with one stroke of a pen, doubled the size of the nascent United States, which at this point was only about two decades old. Wow! But It didn't come about so easily, as you might have guessed already.
 

French/Spanish Louisiane
From the 1680s to the 1760s, the French crown claimed control of Louisiane, a large and undefined swath of land that extended from the Great Lakes to the Gulf of Mexico. The French conducted trade along the rivers of this territory, and forged alliances by establishing trading centers where native villages already stood. The people preferred to work with the French, because they traded guns and were only minimally forcing their religion onto the indigenous populations.

However, the Seven-Years War (named the French-Indian War in US history textbooks) changed the European landscape in North America. The Spanish took control of southern Louisiane, and the English took over New France in today's Canada, in 1762 as the French lost most of their New World footholds. The Spanish methods of settlement, which were focused on salvation and labor for the church and not on mutual economic  beneficence, did not appeal to the people of southern Louisiane. While the Spanish brought administrative advancements to southern Louisiane, they remained mostly unwelcome by the people who preferred dealing with the French.
 

Diplomatic Access
The United States, which formed out of English colonies east of the Mississippi River in 1783, had established a new government by the 1790s and were not eager, or ready, for any territorial expansions that involved European superpowers. Instead, this new country used diplomacy to negotiate access to trade. In 1795, the US gained trading access by New Spain through the Treaty of San Lorenzo/ aka Pickney's Treaty, by allowing Americans navigate the Mississippi River all the way to New Orleans.

But Napoleon Bonaparte put a damper on all this. Napoleon, a French general from the revolutionary government, sought to conquer all of Europe. His troops were successful in accomplishing this to some extent, too. The French wrested control of Louisiane back from the Spanish in 1800. This shift included today's Haiti, which was in the throes of a revolution that had generated from a slave revolt. Napoleon needed money to keep the profitable colonies, and was willing to shed some lands.

Upon learning that the French had regained claim to Louisiane, the third U.S. president, Thomas Jefferson, sent envoys to Paris to renegotiate the Treaty of San Lorenzo. The diplomats even had the authority to purchase New Orleans if negotiations came to that. Instead, the French offered the U.S. envoys the entirety of Louisiane for $15 million.
 

Louisiane becomes Louisiana
The Jeffersonian government, which was of the pro-French factions of the nascent Democratic Party, was more than ready to seal the deal. However, the opposing Federalist Party insisted that land purchases were not within the constitutional realm of the executive branch. A constitutional crisis emerged that almost made Napoleon sell Louisiane to the Spanish or English or to the Russians, so Jefferson authorized the deal under his treaty powers and then, gained approval from a reluctant Congress, which had to pass the action and then, cough up the money, doing so in 1803.

This transaction effectively took the French out of French Louisiana but also out of Haiti, known back then as Saint Dominique, as Napoleon still couldn't afford to keep troops on the island. Their withdrawal established Haiti, the second constitutional republic in the western hemisphere, in 1804. However, to keep in France's and the American slave holders good graces, the U.S. refused to acknowledge Haiti's legitimacy, causing political fallout that can be witnessed to this very day.*

The largest real estate transaction in history (up to that point) thus introduced the Red River of the South to the United States. Learn how much of this unfolded in the articles below!

* The United States would not have become the US without the Kingdom of Morocco, which was the first foreign nation to recognize the U.S.