During the time when North America was still being settled by European colonists, it was possible for settlers to go west and to claim land. The east coast was the first part of North America to be colonized by Europeans (being closest to Europe), so that land was the first to be claimed. After all the land was claimed in the east, there remained land in the west, still available to be claimed (given that the prior claims of native Americans were generally ignored).
rocky mountains
Proclamation of 1763
You could be thinking of the railroad.
Trappers and mountain men were instrumental in exploring and settling the land west of the Mississippi. They had survival skills, and taught them to the new inhabitants of the Wild West.
The proclamation of 1763 simply banned the colonists from settling west of the Allegheny Mountains. It was issued as an attempt to work out a peaceful agreement with the Native American tribes living in the west. The colonists, however, completely ignored the proclamation and continued attempting to colonize the west.
The occupation of land
The award of large land grants to the railroads
MORMONS
Free blacks
The women of the west played a major role in settling.
The mounties, Canadian mounted police, provided law enforcement.
The settling of the west.
Ease of transportation
rocky mountains
Rocky mountains
rocky mountain
Pioneers settling in the Old West.