First, Caesar had a policy of extremely generous mercy towards his opponents in the civil war - he wanted to avoid appearing as a tyrant, and pardoned almost all of his enemies without preconditions, not even a pledge of support. This was an extremely powerful tool to exercise, as it made resisting Caesar less appealing than surrendering - if you lose nothing by surrender, not even your honor, and your cause appears hopeless… why not?

TBF, he also pretty famously found out why a little bit of terror and keeping enemies down could have been a good idea.