To understand ISIS, you have to understand the difference between terrorists and Islamic terrorists.
Ordinary terrorists have two goals; to compel the enemy to meet their political demands and to rally their supporters to consolidate their class, race or national identity group behind them.
Islamic terrorists are not interested in the “political demands” part. They will occasionally accept concessions and even offer Hudnas, temporary truces, but no permanent separate peace can be achieved with them. It’s why Israel’s peace process with terrorists has gone on failing for decades. It’s why the attempt by Gaddafi to achieve peace with the LIFG ended in a civil war and his death. It’s why Obama’s attempts to negotiate with the “moderate Taliban” failed miserably.