Which conclusion about the election of 1860 is BEST justified by the fact that there were four major candidates?

The root cause was the break-up of the old parties by the slavery question.

The Whigs split in 1856 and did not field a candidate. A new party, the Republicans was formed from northern Whigs and anti-slavery factions. The southern whigs and others Southerners formed a new Constitutional Union Party. The Democrats split into north and south and nominated two candidates.