I would ironically shoot war. Despite several earlier assertions that resource scarcity is the main cause of war, I must disagree. Nationalism (religious fundamentalism is a form of nationalism) has been the primary cause of war. Certainly this was the case in the twentieth century. War is more dehumanizing than hunger, and ending it would free up more resources to fight hunger. Economic and social development tends to deal with the population problem far better and, need I really mention, more humanely than war.