A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
deu 7:1ALL COMMUNION WITH THE NATIONS FORBIDDEN. (Deu. 7:1-26)
the Hittites--This people were descended from Heth, the second son of Canaan (Gen 10:15), and occupied the mountainous region about Hebron, in the south of Palestine.
the Girgashites--supposed by some to be the same as the Gergesenes (Mat 8:28), who lay to the east of Lake Gennesareth; but they are placed on the west of Jordan (Jos 24:11), and others take them for a branch of the large family of the Hivites, as they are omitted in nine out of ten places where the tribes of Canaan are enumerated; in the tenth they are mentioned, while the Hivites are not.
the Amorites--descended from the fourth son of Canaan. They occupied, besides their conquest on the Moabite territory, extensive settlements west of the Dead Sea, in the mountains.
the Canaanites--located in PhÅnicia, particularly about Tyre and Sidon, and being sprung from the oldest branch of the family of Canaan, bore his name.
the Perizzites--that is, villagers, a tribe who were dispersed throughout the country and lived in unwalled towns.
the Hivites--who dwelt about Ebal and Gerizim, extending towards Hermon. They are supposed to be the same as the Avims.
the Jebusites--resided about Jerusalem and the adjacent country.
seven nations greater and mightier than thou--Ten were formerly mentioned (Gen 15:19-21). But in the lapse of near five hundred years, it cannot be surprising that some of them had been extinguished in the many intestine feuds that prevailed among those warlike tribes. It is more than probable that some, stationed on the east of Jordan, had fallen under the victorious arms of the Israelites.
deu 7:2thou shalt smite them, and utterly destroy them; thou shalt make no covenant with them--This relentless doom of extermination which God denounced against those tribes of Canaan cannot be reconciled with the attributes of the divine character, except on the assumption that their gross idolatry and enormous wickedness left no reasonable hope of their repentance and amendment. If they were to be swept away like the antediluvians or the people of Sodom and Gomorrah, as incorrigible sinners who had filled up the measure of their iniquities, it mattered not to them in what way the judgment was inflicted; and God, as the Sovereign Disposer, had a right to employ any instruments that pleased Him for executing His judgments. Some think that they were to be exterminated as unprincipled usurpers of a country which God had assigned to the posterity of Eber and which had been occupied ages before by wandering shepherds of that race, till, on the migration of Jacob's family into Egypt through the pressure of famine, the Canaanites overspread the whole land, though they had no legitimate claim to it, and endeavored to retain possession of it by force. In this view their expulsion was just and proper. The strict prohibition against contracting any alliances with such infamous idolaters was a prudential rule, founded on the experience that "evil communications corrupt good manners" [Co1 15:33], and its importance or necessity was attested by the unhappy examples of Solomon and others in the subsequent history of Israel.
deu 7:5thus shall ye deal with them; ye shall destroy their altars, &c.--The removal of the temples, altars, and everything that had been enlisted in the service, or might tend to perpetuate the remembrance, of Canaanite idolatry, was likewise highly expedient for preserving the Israelites from all risk of contamination. It was imitated by the Scottish Reformers, and although many ardent lovers of architecture and the fine arts have anathematized their proceedings as vandalism, yet there was profound wisdom in the favorite maxim of Knox--"pull down the nests, and the rooks will disappear."
deu 7:6For thou art an holy people unto the Lord thy God--that is, set apart to the service of God, or chosen to execute the important purposes of His providence. Their selection to this high destiny was neither on account of their numerical amount (for, till after the death of Joseph, they were but a handful of people); nor because of their extraordinary merits (for they had often pursued a most perverse and unworthy conduct); but it was in consequence of the covenant or promise made with their pious forefathers; and the motives that led to that special act were such as tended not only to vindicate God's wisdom, but to illustrate His glory in diffusing the best and most precious blessings to all mankind.
deu 7:11Thou shalt therefore keep the commandments, and the statutes, and the judgments, which I command thee this day--In the covenant into which God entered with Israel, He promised to bestow upon them a variety of blessings so long as they continued obedient to Him as their heavenly King. He pledged His veracity that His infinite perfections would be exerted for this purpose, as well as for delivering them from every evil to which, as a people, they would be exposed. That people accordingly were truly happy as a nation, and found every promise which the faithful God made to them amply fulfilled, so long as they adhered to that obedience which was required of them. See a beautiful illustration of this in Psa 144:12-15.
deu 7:15the evil diseases of Egypt--(See Exo 15:26). Besides those with which Pharaoh and his subjects were visited, Egypt has always been dreadfully scourged with diseases. The testimony of Moses is confirmed by the reports of many modern writers, who tell us that, notwithstanding its equal temperature and sereneness, that country has some indigenous maladies which are very malignant, such as ophthalmia, dysentery, smallpox, and the plague.
deu 7:20Moreover the Lord thy God will send the hornet among them--(See on Jos 24:12 [and Exo 23:28]).
deu 7:22lest the beasts of the field increase upon thee--(See on Exo 23:29). The omnipotence of their Almighty Ruler could have given them possession of the promised land at once. But, the unburied corpses of the enemy and the portions of the country that might have been left desolate for a while, would have drawn an influx of dangerous beasts. This evil would be prevented by a progressive conquest and by the use of ordinary means, which God would bless.