split up vs unify

split up

verb
  • separate, disassociate, cause to come apart. 

  • Cease to be together, break apart from the group. 

adj
  • Divided or separated. 

unify

verb
  • Cause to become one; make into a unit; consolidate; merge; combine. 

  • Become one. 

How often have the words split up and unify occurred in a corpus of books? (source: Google Ngram Viewer )