Afghanistan in 2001 was just but the way the Bush administration pursued the war was unjust. Thus the war in Afgahanistan achieves jus ad bello but not jus post bellum. Walzer goes further and argues that the most compelling argument for the war in Afghanistan is not necessarily strategic arguments but rather the moral and political argument, "that we owe the Afghan people eight years after we invaded their country." Walzer goes on to outline the improvements that have been brought to the Afghan people including schools, organizations, social group etc that are participating in a, "new, largely secular, civil society."
All in all the argument Walzer makes is interesting but I'm reminded of the words of Hans Morgenthau, "There can be no political morality without prudence; that is, without consideration of the political consequences of seemingly moral action. Realism, then, considers prudence--the weighing of the consequences of alternative political actions--to be the supreme virtue in politics."
There seems to be two strands of jus post bellum in terms of Afghanistan maybe the broader concept of jus post bellum: justice where the war is fought and justice in the country fighting. That is how much risk in blood and treasure does the occupying country risk in order to create the institutions and civil society needed for success in the occupied country. Is there a limitless supply of resources and time for insuring the civil society and institutions in Afghanistan? Interesting stuff.