Why was the election of 1860 so controversial?

The 1860 Republican National Convention, in Chicago, nominated Lincoln, a moderate former one-term Representative from Illinois, as its standard-bearer. Its platform promised not to interfere with slavery in the Southern states but opposed the further extension of slavery into the Western territories.The Republican Party was relatively new; 1860 was only the second time the party had a candidate in the presidential race. The Constitutional Union Party was also new; 1860 was the first and only time the party ran a candidate for president. The results of the 1860 election pushed the nation into war.

i see, would you mind putting it as one?