While most of the people below had some good points, there's another simple reason: Because they wanted to. Puppets can do a lot of things that humans or animals can't. They can evoke emotions that human/animal actors might not.
They can be made to do things that human/animals can't (or won't). Here's some reasons why people use puppets in general: http://www.schoolofpuppetry.com.au/tutor... Having said that, why not ask the question of another medium? Why didn't they use ballet dancers?
Why didn't they use circus? ... At the end of the day, it has to do with a lot of different things. Budget, personal tastes from the director, marketability, etc. But most importantly would be the way in which puppets complement the story.
There's also another issue: why go to the theatre to see exactly was in the movie? They have to make it different somehow, especially if they want people to pay for a ticket rather than buy a DVD of the movie. So puppets are a good way to differentiate themselves from the movie, whilst still attracting interest in the same story.
Ryan has a strange point: since when is making a large puppet and shipping it around the world, cheaper? If nothing else, you have to spend time and money designing, building and repairing the puppet, let alone training people to use it. I doubt the costs of making a puppet would greatly outweigh the costs of using a trained horse.
(For example, check out "How to Train Your Dragon" the stage show. It tours with some 60 crew, about 30 cast, uses 40-50 trucks, and has an extra 100 crew available when setting/packing up. Exchange that for a few horses.... and see what costs less) Ilovemyfatcat also has an odd point: no one really uses sharp objects on stage.
Real barbed wire? Not unless they want to have their funding/insurance removed. Actors can get hurt too you know.
Animals shouldn't be used in movies at all. They are usually mistreated when they are at the same time as they make it much more difficult to work with. Animals can't be told directly what to do so it's much easier to use CGI (Such as the apes in Rise of the Planet of the Apes).
It's also less expensive because you also have to pay a trainer to work with the animal.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.