Growing Influence.

Although less than three hundred thousand people voted for the Free Soil Party in 1848, these antislavery partisans exerted an influence on the national political agenda that far outpaced their numbers. Topping the list of priorities for Free Soilers, of course, was keeping slavery out of the western territories acquired from Mexico. Many Whigs and Democrats disagreed: they preferred to keep the explosive question of slavery in the territories on the political sidelines, but the discovery of gold near Sacramento, California, in 1848—causing the thousands of prospectors who headed west the following year—made postponing the issue impossible. The political crisis over whether the North or the South would control the settlement of the former Mexican lands almost tore the nation apart in 1850.

California Gold Rush.

At first Easterners were skeptical about the gold-flecked rumors spreading...