The history of a nation, like that of an individual, begins from the moment it becomes an independent entity capable of making its own decisions. The giving of the Torah at Sinai and the wanderings through the wilderness were only the prehistory of the Jewish people. Their true story begins with the conquest of the Land.
The generation that Moses led out of Egypt had to be managed by directive. Their movements were determined by a pillar of cloud by day and a pillar of fire by night, and Moses too gave them orders, so that they knew what to do. Even the giving of the Torah at the Sinai, according to the Midrash, happened under conditions of duress, and the Jews accepted the Torah only on that basis.
“And they took their places at the foot of the mountain” (19:17, but literally, “They stood on the underside of the mountain”). The Talmud expands on this: “Rabbi Abdimi b. Hama b. Hasa said: This teaches that the Holy One, blessed be He, overturned the mountain upon them like an inverted cask, and said to them, ‘If ye accept the Torah, ‘tis well; but if not, there shall be your burial.’ ” (Shabbat 88a).
By the time the nation was about to cross the Jordan River under Joshua’s leadership, the cloud and the pillar of fire were already departing, as was Moses too, and in a sense the people were now left to fend for themselves. We could say that at this point in history the Jewish people had finally completed their course of academic study (Mount Sinai and the Wilderness), and were leaving their cloistered existence to go out into the real world for the very first time, to begin a life of self-sufficiency and independence. Jewish history begins when the nation is finally in a position to decide its own fate, to make decisions and be responsible for its actions – by solving on its own the problems that it creates.
But in order for this new era to begin, Moses had to leave the scene.
 For more on this topic, see our commentary later, on verse 19:17.