If he had told sasuke then itachi's true plans would have failed cuz itachi wanted sasuke to hate him. Itachi wanted sasuke to become the hero who avenged his clan and the man who killed Konoha's traitor. If it weren't for Tobi, Itachi's plans would have succeeded, he never intended for sasuke to want to crush Konoha.to stop a war...yes... but he should told sasuke atleast