C. F. Keil and Franz Delitzsch on 2 Chronicles 20:10-12

2Ch 20:10-12 ועתּה, and now, the contrary of this has occurred. Peoples into whose midst (בהם לבוא...אשׁר) Thou didst not allow Israel to come, i.e., into whose land Thou didst not allow Israel to enter when they came out of the land of Egypt, for they (the Israelites under Moses) turned from them and destroyed them not (cf. as to the fact, Num 20:14.; Deu 2:4; Deu 9:19); behold, these peoples recompense us by coming to cast us out of our possession which Thou hast given us (הורישׁ, to give as a possession, as in Jdg 11:24). There follows hereupon in 2Ch 20:12 the prayer: “Our God, wilt Thou not judge,” i.e., do right upon them, for we have not strength before (to withstand) this multitude? We know not what to do, sc. against so many enemies; but our eyes are turned to Thee, i.e., to Thee we look for help; cf. Psa 123:2; Psa 141:8.