Jericho was just the opening salvo in God's long-established plan to judge the Canaanites.  400 years earlier, God said to Abraham:

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         "In the fourth generation your descendants will come back here, for the sin of the Amorites has not yet reached its full measure" (Gen 15:16).

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          So God Himself was waiting upon man, sinful man, for the ripening of all man's evil desires.  And then He would act decisively to judge them.

       

We see in the dramatic campaign against Jericho a replay of the devastation visited upon Egypt 40 years before.  It was a religious pageant which was unfolding, and the people were merely actors on a cosmic stage.  Just as the crescendo of plagues built to a climax in Egypt, at Jericho the 7 days of marching had the same effect, culminating in a great shout, the collapse of the walls, and the killing of all people and animals in the city.  This was a divine parade, a display, a taunting of the gods of Canaan on the part of Yahweh.  He would gain victory over them through His people marching and blowing trumpets.  The destruction of the city represented the desecration of the seat of power of the idols.  The children and animals were slaughtered for the same reason that the eldest sons of the Egyptians were killed -- it was guilt by affiliation.  In contrast to the modern world-view, which postulates "original innocence" in each individual, the Bible teaches that ancient peoples were owned by the gods they worshipped.  Deity and nation were linked together, inseparably.  The only way to overthrow the idols was to destroy their human devotees.