Aconnection between northern democrats, free-soilers, and conscience whigs in 1854 was that they

Each of these parties did not support slavery.

Northern Democrats split from the Democratic Party over slavery.  Southern Democrats still avidly supported slavery in 1854.

Free-Soilers were mostly small farmers who did not support slavery because it hurt their enterprise.  It was difficult to compete with slave owners.

Conscience Whigs did not support slavery because they believed it was morally wrong, hence the "conscience" designation.

Hope this helps!!

the american civil war was not caused   by slavery but by economic factors.