It's easy to forget in our media rich world that at the time these wars took place, information was very much controlled by the governments of the country.
The people were, to be blunt, ignorant of the truth and they not only relied on the ruling bodies to tell them what was happening but how they should behave. If there was need of people for war then it was "the duty of all good (insert nationality of choice) to join up and teach the dirty (insert nationality of choice) a bloody good lesson."
It's only in these later years that people are beginning to not only understand other nations and cultures, but to appreciate them. I'd like to think that those few men in power are running out of excuses to get the people to do their bidding, but I think we've a way to go yet.
It's interesting to note that in these modern times, we can talk about how current governments and authorities conspire to hide truths and tell lies, but at the time of these conflicts we wouldn't even have considered such activities were taking place. In fact, anyone voicing any such concerns could be punished for treason or sedition.