Kautilya's Arthashastra 7.4.19

7.4.19

yadā vā paśyet "na śakyam ekena yātum avaśyaṃ ca yātavyam" iti tadā samahīnajyāyobhiḥ sāmavāyikaiḥ sambhūya yāyād, ekatra nirdiṣṭenāṃśena, anekatrānirdiṣṭenāṃśena //

When a king finds himself unable to confront his enemy single-handed and when it is necessary that he should march, then he should make the expedition in combination with kings of inferior, equal, or superior powers.

When the object aimed at is of a definite nature, then the share of spoils should be fixed; but when it is of a manifold or complex nature, then with no fixity in the share of the spoils. When no such combination is possible, he may request a king either to supply him with the army for a fixed share, or to accompany him for an equal share of the spoils.