The Kansas-Nebraska Act
caused a tremendous northern protest and the birth of the Republican Party.
Stephen Douglas' indifference to slavery and desire for a northern railroad route
led to the passage of the Kansas-Nebraska Act, without regard for the consequences.
The Gadsden Purchase
heightened competition between southern and norther railroad promoters over the choice of a transcontinental route.
The Pierce administration's schemes to acquire Cuba
fell apart after the leaking of the Ostend Manifesto.
The Fugitive Slave Law
aroused active northern resistance to legal enforcement and prompted attempts at nullification in Massachusetts.
The Compromise of 1850
created a short-lived national mood of optimism and reconciliation.
The Free-Soil part
was the predecessor of the antislavery Republican Party.
The Underground Railroad
aroused southern demands for an effective fugitive-slave law.
The California gold rush
made the issue of slavery in the Mexican Cession areas more urgent.
The evasion of the slavery issue by Whigs and Democrats in 1848
led to the formation of the new Free-Soil antislavery party.