What issue decided the 1848 election?

A) Tariff rates
B) The conduct of the War with Mexico
C) Slavery in the territories
D) The independent Treasury bill

The issue of slavery in the territories, specifically whether it should be allowed or not, was the main issue that decided the election of 1848. The major parties, the Democrats and the Whigs, were divided on this issue, with the Democrats supporting popular sovereignty (allowing the territories to decide for themselves) and the Whigs supporting the Wilmot Proviso (banning slavery in the territories). The newly formed Free Soil Party also ran on an anti-slavery platform, further emphasizing the issue's importance in the election.