The first thing that came to mind was the nature of the war in question. Vietnam and increasingly Iraq are both unpopular wars with the conflict removed from dynamic action toa bogged down guerilla war. This could equate similarly to the trench warfare of the first World War. Why is this of any interest? A righteous war, one with great victories and against a great foe I would imagine would produce few restless dead. While death is not often desired, falling to combat a worthy foe is not seen as dishonorable, so their shades would be less inclined to linger on. Against a low and mean emeny without clear paths to victory, and with poor morale, those who fall are not filled with sense of pride, duty, service to family, country, and god, instead they are angry and bitter about fighting what they feel is a pointless war.
So start with a meat-grinder war, the sort that consumes men and material with no real progress other than the tripe spewed by the politicoes on both sides. The soldiers are disenfranchised, dissatisfied with the war, and they die. This fuel of spiritual angst in a proper magical setting should be enough to produce ghosts driven to fight and fight without sense or purpose, without end as this was the mode of their life at the moment of death.
I hope that helps.
There will be a test.