Unlike Moses, Joshua seems not to have consulted G-d to find out who would lead the Jewish People after his death. Where can I find commentary about why the change from a single leader (necessary for the conquest of the Promised land and the distribution of the Land to each tribe?) to the ‘group’ responsibility implicit in Joshua’s succession was made at this point?
First of all, I think that most of the answer is implicit in your own words: “necessary for the conquest of the Promised land and the distribution of the Land to each tribe?”
I will suggest that the natural and expected state of Jewish national political life upon settling the Land was summarized in Judges 17: 6 and 21: 25 (among others, unless I’m mistaken). While it is true that there is a hint of criticism in those words – as though no one listened to HaShem’s will – nevertheless, I believe that the implied freedom and loose national structure were an opportunity for self-development in preparation for monarchy. That, according to Rabbi S.R. Hirsch, was why the Jews in the time of Samuel the Prophet were criticized for having asked for a king too soon – despite appointing a king being a Torah obligation. Therefore, once the tribes were largely settled and the rhythm of Torah life was established, Jews could move on to the next, crucial stage of their development: autonomy. In fact, through the 400-year period of the judges, there was no central authority of any sort in Israel – perhaps not even a national Sanhedrin (High Court).
Joshua likely still needed the extra authority available through G-d’s explicit backing in order to divide the land – something that would otherwise sink into a morass of politics and resentment. Once that was done, each Jewish family was left to rise on its own to full and happy Torah living.
I hope this helps. With my regards,
Rabbi Boruch Clinton