merge vs split up

merge

verb
  • To blend gradually into something else. 

  • To combine into a whole. 

noun
  • The joining together of multiple sources. 

split up

adj
  • Divided or separated. 

verb
  • separate, disassociate, cause to come apart. 

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

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