Arthashastra
अमित्र सिद्धौ हि यातव्यः साहाय्यं दद्यान् न अमित्रो यातव्य सिद्धौ ॥
The strong enemy is to be marched against first; after vanquishing him, the assailable enemy is to be attacked, for, when a strong enemy has been vanquished, an assailable enemy will volunteer of his own accord to help the conqueror; but not so, a strong enemy.
english translation
amitra siddhau hi yAtavyaH sAhAyyaM dadyAn na amitro yAtavya siddhau ॥
hk transliteration by Sanscript