Judges 2:2

League. None of a public nature had been perhaps made by the whole nation, to sanction the idolatry of the Chanaanites. But so many individuals had entered into marriages with them and imitated their perverse manners, so many tribes had spared the cities, &c., that the Israelites in general merited the reprimand. Whether these leagues, made in contradiction to God's command, where to be observed or broken, in a matter of dispute. We may steer a middle course, and assert that such agreements as stipulated the protection of the idolatrous worship and altars, were null, and never to be observed; whereas those which secured to the inhabitants their lives and property, could not be lawfully broken, though the contractors did wrong in making such leagues. See 1 Esdras ix. (Calmet)