Adam Clarke on Judges 6:4

Encamped against them - Wandering hordes of Midianites, Amalekites, and Ishmaelites came, in the times of harvest and autumn, and carried away their crops, their fruit, and their cattle. And they appear to have come early, encamped in the plains, and watched the crops till they were ready to be carried off. This is frequently the case even to the present day.

Till thou come unto Gaza - That is, the whole breadth of the land, from Jordan to the coast of the Mediterranean Sea. Thus the whole land was ravaged, and the inhabitants deprived of the necessaries of life.