The city often referred to as the "Gateway to the West" is St. Louis, Missouri, in the United States. This nickname is a tribute to St. Louis's historical significance as a crucial gateway and starting point for westward expansion during the 19th century in the United States.

The city's role as the "Gateway to the West" is closely associated with the westward expansion of the United States during the 1800s, particularly during the era of westward migration, exploration, and settlement. St. Louis was a pivotal hub for pioneers, settlers, and explorers who ventured beyond the Mississippi River into the largely uncharted territories of the American West.

Several key factors contributed to St. Louis earning this nickname:

1. Geographical Location: St. Louis is strategically located along the western bank of the Mississippi River, which served as a natural barrier and obstacle for those heading westward. The city served as the last major urban center and supply point before settlers and explorers embarked on their westward journeys.

2. Starting Point for Expeditions: Numerous famous expeditions, such as the Lewis and Clark Expedition led by Meriwether Lewis and William Clark in the early 1800s, began their westward journeys from St. Louis. The city provided a launching point for these historic missions, which aimed to explore and map the newly acquired western territories of the United States.

3. Trading and Transportation Hub: St. Louis played a pivotal role as a trading and transportation hub, facilitating the movement of people, goods, and supplies westward. The city's location along the Mississippi River made it a crucial stop for riverboat traffic and later, the expansion of railroads.

Today, St. Louis continues to honor its historical legacy as the "Gateway to the West." The Gateway Arch, a 630-foot stainless steel monument located in the city, serves as an iconic symbol of this historical significance. The arch, officially known as the Gateway Arch National Park, commemorates the westward expansion of the United States and stands as a testament to the pioneers and explorers who embarked on journeys of discovery and settlement in the American West.