The phrase "to destroy the union" refers to actions or intentions that aim to break apart or dissolve a group of states or territories that are united under a common government. Full definition
By his mere great power on the minds of the now contestants, he could have either saved or destroyed the Union without a human contest. (religion-online.org)
Hmmm, let's see: In the 1980's, Wall Street firms destroyed unions and left millions of Americans unemployed by engaging in leveraged buyouts. (nyc.streetsblog.org)
Let us not split into factions which must destroy that union upon which our existence hangs.» (courant.com)