The Buddha was against violence. But he was also in favour of justice and where justice required he permitted the use of force. This is well illustrated in his dialogue with Sinha Senapati the Commander-in-Chief of Vaishali. Sinha having come to know that the Buddha preached Ahimsa
went to him and asked:
“The Bhagvan preaches Ahimsa (Nonviolence). Does the Bhagvan preach an offender to be given freedom from punishment? Does the Bhagvan preach that we should not go to war to save our wives, our children and our wealth? Should we suffer at the hands of criminals in the name of Ahimsa?”
“Does the Tathagata prohibit all war even when it is in the interest of Truth and Justice?”
Buddha replied. “You have wrongly understood what I have been preaching. An offender must be punished and an innocent man must be freed. It is not a fault of the Magistrate if he punishes an offender. The cause of punishment is the fault of the offender. The Magistrate who inflicts the punishment is only carrying out the law. He does not become stained with Himsa (Violence). A man who fights for justice and safety cannot be accused of Himsa. If all the means of maintaining peace have failed then the responsibility for Himsa falls on him who starts war. One must never surrender to evil powers. War there may be. But it must not be for selfish ends…”
(Source: Buddha or Karl Marx by Ambedkar)
Know Thyself 