[A nod of understanding. Sari knew things were probably even stranger in her world than Mikaela's. This was weird in a sense, but comforting knowing someone was familiar with the Autobots.]
From what I remember, the Decepticons had been exiled from Cybertron after the Great War millennia ago. But the war was revived when the AllSpark was discovered. Optimus and the others were working on repairing a space bridge when they found it.