Fort Laramie (founded as Fort William and then known for a while as Fort John) was a significant 19th century trading post and diplomatic site located at the confluence of the Laramie River and the North Platte River in the upper Platte River Valley in the eastern part of the U.S. state of Wyoming.

It was founded in the 1830s to service the overland fur trade during the middle 19th century. It sat at the bottom of the long climb leading to the best and lowest crossing point at South Pass into western descending valleys and so was a primary stopping point on the Oregon Trail. Along with Bent's Fort on the Arkansas River, the trading post and its supporting industries and businesses were the most significant economic hub of commerce in the region.

More Info: en.wikipedia.org