The Louisiana Purchase of 1803, which quadrupled the country's area, was the first big expansion of the country, while the southeastern boundary with Spanish Florida was a source of contention until it and Spanish claims to the Oregon Country were given to the US in 1821. The discovery of gold in California in 1848 started the second major phase of American expansion, which ended with the admission of the last state, Hawaii, into the Union in 1898.
All together, the United States acquired over 11 million acres (44,000 km2) of land. Today, that would be equivalent to adding another California to the country.
In addition to Louisiana, other examples of acquisitions include all of North America beyond the original 13 colonies. The Louisiana Purchase was paid for in part with money from a national bank proposed by Thomas Jefferson but not approved by Congress.
The third phase of American expansion began after the War of Independence with the settling of the West. This era concluded around 1890 with the arrival of the railroad and the start of the Industrial Revolution. It increased productivity, which allowed farmers to sell their products at higher prices than those available in Europe, encouraging more production.
At the end of this period, around 1930, the United States owned nearly half of the total acreage allocated to farming in the world.
The Louisiana Purchase, for $10 million, was the country's first and greatest territory purchase; it roughly quadrupled the area of the original 13 states. The Mariana Islands, Caroline Islands, and Marshall Islands were the most recent U.S. territorial acquisitions as of August 2019. These areas were purchased from Japan after its defeat in World War II.
The question usually comes down to how you count territories. The conventional view is that Louisiana was acquired in 1803 so the answer is 2003. But some scholars argue that the Republic of Texas became the 23rd state in 1845 not 1803. If they are right then the correct answer is 1945 instead of 2003.
Here is why they might be right: When Texas joined the Union on March 4, 1845 it was not part of the United States but rather a separate country called the "Republic of Texas". However, when the Civil War broke out six years later, Texas quickly aligned itself with the Confederacy and received full recognition as a sovereign nation once more. After the war, Texas agreed to be re-admitted into the Union on May 11, 1869.
This all means that Texas was back in federal jurisdiction again, and thus the 1945 vote to admit it into the military service program was actually the moment that it regained its status as a state.
Table of territory conquests by the United States
|Louisiana Purchase, from France||1803||827,987|
|Florida (East and West), purchased from Spain||1819||72,101|
|Oregon Territory, by treaty with Great Britain||1846||286,541|
By 1820, the United States had expanded well beyond its original borders. The nation's frontiers shifted west to the Rocky Mountains, north to the 49th parallel, and south to Florida and the Gulf of Mexico as a result of the Louisiana Purchase in 1803 and treaties with Spain and Britain.
In addition, the government granted land patents to any person who explored or settled areas now part of the United States. These grants often included large sections of land, which led to the expansion of border settlements.
For example, the Lewis and Clark Expedition crossed into what would later become Montana in 1806. In return for their services as guides for several American politicians, the men were given land along the Missouri River. The expedition returned home in 1809, but the settlement they founded - called Jefferson City after Thomas Jefferson - grew quickly due to the federal government's policy of granting land patents to anyone who arrived at their destination first. By 1821, Jefferson City was the largest city on the Missouri River between St. Louis and Fort Benton, British-owned Canada.
Other settlements along the Missouri River received similar treatments, leading to the growth of many large cities across the middle of the country. For example, Kansas City began as a settlement called Shawnee Town before it was abandoned by the local tribe in 1838 but soon after was rebuilt by immigrants from Germany and Ireland.
The Louisiana Purchase effectively quadrupled the size of the United States, substantially strengthened it materially and tactically, gave a major incentive to westward development, and established the theory of implied powers in the federal Constitution. The purchase also opened up vast areas of land for settlement by Europeans.
This expansion occurred because President Thomas Jefferson sought to acquire new territory for America. He believed that living free would ensure American prosperity and prevent any one nation from dominating the world stage. Land acquisition was only one part of this plan; the president also wanted to encourage immigration to the United States. In order to do this, he offered a reward of $7.5 million for anyone who could locate a passage to the West Coast from anywhere within the continent. This offer, known as the Lewis and Clark Expedition Fund, helped support two explorers who were chosen by Congress to travel across the country and report on what they found there.
When these men returned from their expedition, they presented a report to Congress outlining five possible routes for future expeditions. Jefferson immediately took action on this recommendation, and on April 18, 1803, signed a document authorizing the sale of this land.