Once you complete The Dogs of War mission, there are chances you won't find any new main missions. The next mission is Hammer of the Gods. To unlock this mission you need to first purchase "A mysterious Marauder device - Nano Forge". Without which there won't be any progress in the game, i.e. no new main mission.
Similarly, there is one more turn, wherein you need to purchase "Radiation Shielding" or else you cannot proceed with the next mission "Meeting the Marauders". You will die for sure before entering the area.
Some good walkthrough links:
http://wikicheats.gametrailers.com/Red_Faction:_Guerrilla_-_PC_PS3_XB360/Walkthrough
http://faqs.ign.com/articles/100/1005448p1.html
http://guides.gamepressure.com/redfactionguerrilla/guide.asp?ID=7608
