The answer to this question depends on perspective. For whites seeking economic opportunity, the settling of the West was, by and large, a story of liberty, opportunity, and progress. People who had few opportunities in the established eastern states took advantage of the opportunity that cheap land provided.
For others, however, it was quite different. In the Deep South, for example, as whites swarmed into territories in Alabama, Mississippi, and western Georgia, they secured the assistance of state and federal governments in dispossessing Indian peoples of their lands. This opened up an enormous demand for slaves, who were forcibly carried from Virginia in what became a massive internal slave trading system.
There was also the Mexican War, which erupted largely due to the desire of US officials to gain Mexican lands, which southerners hoped to fill with slaves. Indeed, by the end of the Mexican War, the "manifest destiny" of the United States to expand westward to the Pacific had been fulfilled. In the old Northwest, patterns of expansion were similar, though Indian peoples in this region resisted incursions by Americans.
In short, the considerable liberty, opportunity or progress that came as a result of westward expansion was accompanied by the exploitation of black labor and the expropriation of Native American and Mexican lands.