Outside the "tumbled-down walls"Perhaps most scholars would agree that many of the narrative in the Bible are based in reality if one squints: some are actually several real events that have been tied together, the reality is inaccessible because we cannot understand the language completely, the magnitude some facts have been exaggerated over time, etc.
The Book of Joshua is one huge puzzle. No archeologist has found evidence of a rapid military takeover of the Levant by an invading/migrating people. In particular, the walls of Jericho did not collapse in a military siege, and the city of Ai was already ruined when the Hebrews arrived. Instead, the archeological record shows a benign process of transition. During the thirteenth and twelth centuries BC Judaic practices (especially dietary) gradually spread throughout the settlements in Canaan. As a Jew it is a relief that my ancient ancestors cannot be called occupiers, but it is puzzling that the Book of Joshua could be so wrong.
One of the explanations is interesting because it deals with issues of frontiers and decentralization. Canaan had come under the control of Egypt around the 16th and 15th centuries BC. The New Kingdom was an aggressively militaristic power--Egypt had come out of a period in which immigrants (Hyksos) had become an alternative society within Egyptian society. The New Kingdom kings resolved to prevent foreign influences within Egypt by projecting force outside of Egypt--they engaged in wars with neighboring powers in Asia as far away as the Euphrates.
In the Levant they set up clients states: Egyptian governors with small garrisons ruled through native vassals. The cities became sites of power in which local Canaanite aristocracies controlled peasants. The power of the aristocracies depended on their relationship with Egyptian governors. This system of indirect rule stabilized Egypt's Asian frontier for several centuries.
Egyptian imperial power declined in the 12th and 11th centuries BC: its resources dwindled (especially gold from Nubia); the length of reign of kings shortened; there was corruption. With the contraction of power stability on the Asia frontier destabilized.
The theory of decentralization proposes that the weakening of imperial power also weakened the influence of the vassals-aristocracies over the peasantry. Some peasants escape the control of the cities and established their own settlements outside the sphere of power of the aristocracies. These communities established new social and cultural norms that contradicted Canaanite standards. In particular, they emphasized social equality within the community (there was no aristocracy).
If the theory is credible, the takeover was a benign process occuring against an imperial power.