The Mother of Inventions

A young lady of my acquaintance has been having a problem with her imaginary friends. Some sort of epidemic seems to have swept through them, because one by one they've been dying off. She announced yesterday that all but one her imaginary friends were dead, and that she was going to have to make up some more (of course she knows she made them up — she's 3, not stupid).

In her case, it's easy to understand what's going on. Her grandmother died recently, and this is one way that she's been processing that, in a perfectly age-appropriate way. The games she plays with her older sister have also reflected this process; many of their characters seem to have been recently bereaved.

But what motivated the people who invented Sgt Dan Kennings, used him for two years of anti-war propaganda, and eventually killed him off?