TF2 Blog: "So: how is the War update different from our other class updates?
In many ways, it's not. Like any other class update, the War update will reveal three new weapons each for the Demoman and Soldier throughout the week, as well as some maps, achievements, and surprises, right up until the day of release, when everything we've been teasing goes live..."
In short, show your support for each class by logging on to TF2 and kill each other. Which ever class, Demoman or Soldier, has the most kills on one another by next week gets an extra unlock.
Hop to it, Soldier/Demoman!