You may be interested in this answer which /u/XenophonTheAthenian posted last month. The question concerns Pompeys marriage to Caesars daughter, but XenophonTheAthenian opens his answer with an explanation of the "First Triumvirate".

Crassus pretty much kept Caeser and Pompey from civil war as whoever Crassus sided with would probably win due to his wealth. When Crassus dies it sets Caeser and Pompey on course for civil war