John Calvin Commentary Psalms 78:55

"He drove out the nations also before them, And allotted them for an inheritance by line, And made the tribes of Israel to dwell in their tents." — Psalms 78:55 (ASV)

He expelled the heathen from before them; and made them to fall into their part of the inheritance. These words explain the concluding sentence of the preceding verse, describing how the land of Canaan was acquired.

This description plainly indicates that the Israelites were not such a warlike people, nor were those heathen nations so cowardly, as to make it an easy matter for the former to vanquish the latter. Moreover, it would have been impossible for the former to expel the latter from the country if they had not been led to victory under God's guidance and aided by His power.

Besides, it would have been unlawful for them to take possession of the country if it had not been God's will that the first inhabitants should be deprived of it, and that strangers should be established there in their place.