I've found a good teaser: a past incident during the war for one or another of the characters to build the flavor quickly, then move to the 'introduction', where everyone is brought together. Then hit 'em with some kind of plot/story/whatever.
The teaser always seems to work well. Just keep if taught and quick.
"War is an ugly thing but not the ugliest of things; the decayed and degraded state of moral and patriotic feelings which thinks that nothing is worth war is much worse. A man who has nothing for which he is willing to fight, nothing which is more important than his own personal safety, is a miserable creature and has no chance of being free unless made and kept so by the exertions of better men than himself."
John Stuart Mill