Violence can sometimes bring about peace, as when you defeat and destroy an enemy in battle and thereby bring peace to the land. But such peace may not be long-lasting as the defeated enemy may gather strength and again return to create more havoc. But generally it is true. Long-lasting peace cannot be achieved through violence. Understanding is needed. As far as internal struggles are concerned, the saying is 100% true. Internal conflict can only be resolved through right understanding and right conduct.