Kautilya's Arthashastra 7.13.35

7.13.35

dvayor api purastād dūṣyabalaghātinor yo bahulataraṃ śaktimattaram atyantadūṣyaṃ ca ghātayet so 'tisaṃdhatte //

Loss of men and money being equal, he who entirely destroys first his frontal enemy, and next attacks his rear-enemy gains more advantages; when both the conqueror and his enemy are severally engaged in destroying their respective frontal enemies, he who destroys a frontal enemy of deep rooted enmity and of vast resources, gains more advantages.