The Causes of the Civil War
As American territory expanded, such as with the Mexican Cession, the debate over the expansion of slavery intensified. In the Wilmot Proviso it was proposed that slavery would cease to exist in any territory acquired from Mexico. The proposal failed to make it through Congress and ultimately the Compromise of 1850 opened up popular sovereignty. With California entering the Union as a free state upsetting the balance in the Senate, the South felt more threatened than ever.