A definition of Manifest Destiny, the phrase that became synonymous with the settlement of the American West.
The Erie Canal was the first great artery into the American West, as it allowed people and goods to move from the Hudson River to the Great Lakes, thus providing an entry point to the interior of North America.
The National Road, the first federal highway, provided countless settlers with a means to leave the East Coast and move westward. Started early in the 19th century, it eventually ran from Washington, D.C. to Indiana.
Fort Astoria was an early settlement on the Pacific Coast organized by John Jacob Astor, American's richest man. The trading outpost was not designed to spur settlement, but some of the fur traders, venturing eastward toward civilization, inadvertently discovered trails that would later be used by thousands of settlers heading westward.
The Oregon Trail became a major artery for settlers moving westward. It began in Missouri and ended in Oregon's Willamette Valley. When "Oregon fever" took hold in the 1840s, thousands of pioneer families traveled on the Oregon Trail.
John C. Frémont was a controversial figure who became known as "The Pathfinder" though he did little original exploring on his own. But he did publish reports of what could be found in the West, and his writings, which were really collaborations with his politically-connected wife, inspired many Americans to head westward.
Zebulon Pike headed into the unmapped West early in the 19th century, and there is still some question whether he was an explorer or a spy. Taken into custody when he wandered into Mexican territory, he was suspected of intrigue. But his movements helped shape an understanding of the American southwest.