Mahabharata 12.96.2

12.96.2

bhīṣma uvāca |
sasahāyo'sahāyo vā rāṣṭramāgamya bhūmipaḥ |
brūyādahaṃ vo rājeti rakṣiṣyāmi ca vaḥ sadā || 2 ||

"Bhishma said, 'The king, with or without an army at his back, entering the dominions of the king he would subjugate, should say unto all the people, 'I am your king. I shall always protect you. Give me the just tribute or encounter me in battle.' If the people accept him for their king, there need not be any fighting. If, without being Kshatriyas by birth, they show signs of hostility, they should then, observant as they are of practices not laid down for them, be sought to be restrained by every means. People of the other orders do take up arms (for resisting the invader) if they behold the Kshatriya unarmed for fight, incapable of protecting himself, and making too much of the enemy.'