Russia sold the territory known as Alaska to the US in 1687, but Indigenous people have been living on that land for thousands of years.
One commonly accepted theory was that the first people traveled to North America from Asia via the Bering Land Bridge, although more recent discoveries suggest they made their way by sea.
Russia began colonizing Alaska and other parts of North America in the late 1700s, establishing Russian America and making money off the fur trade. But by the 1860s, the fur trade had declined due to over-hunting.
US critics dubbed the purchase "Seward's Folly," named for then-Secretary of State William Seward because they felt the land, which they called an "icebox," was useless. The transaction was also made against the wishes of some Native Alaskans, who argued it wasn't Russia's land to sell, according to the Alaska Native Foundation.
Three decades later, the Klondike Gold Strike brought thousands of migrants to the territory.
Alaska officially became a state 92 years after the transaction, in January 1959, making it the 49th state. Hawaii became the 50th state that same year.
Now, Alaska is a popular tourist destination, with thousands of people traveling there via cruise each year.
These vintage photos show what Alaska looked like before it became part of the United States.