There's always some blood but for the civilian population the optimal tactic is peaceful noncompliance. Research how Norwegians dealt with Nazi occupation in WWII.

Armies are well versed in dealing with violence and they'll get right to it when you give them an excuse. They get far less efficient when trying to fight sabotage on a million different levels of everyday life. This is fifth generation information warfare, it's not all about pew-pew anymore.