Slytherins would probably turn against each other before achieving anything if one of them wasn't so much more powerful than anyone else.
Ambition, Cunning and Resourcefulness certainly don't rule out the possibility of solving cooperation problems. Even Draco with the lessons Harry has taught him would be sufficient for him to take over the world rather effectively if Harry was out of the way.
World used to be filled with revolutionary movements, and very few managed to grow past Dunbar's number or so before falling apart by everyone trying to out-politic everyone else.
Only very few that were extraordinarily loyal like Bolsheviks won. The primary difference between Bolsheviks and everyone else was their strong belief in strict loyalty to the party, whose decisions were to be absolutely binding upon all members.
Even after they started killing each other, very few defected the Party to join some other group.
Update: This post has also been superseded - new comments belong in the latest thread.
The second thread has now also exceeded 500 comments, so after 42 chapters of MoR it's time for a new thread.
From the first thread: