Hope
It had been a slagging long time since the Autobots had any kind hope that they could end the war, and it had taken Samuel, a human boy, to bring it back to them.
It wasn't because of his bravery, his selflessness, his determination, his totally natural acceptance of them for whom they truly were, or even his actual love for them as people, although those things certainly helped.
No, it was because Sam, as he so easily wound his way into their sparks with his quick tongue and fierce loyalty, had reminded them that they had something to fight for, and that was why they would win this war.