The article 'de' should not be included in the dutch sentence or 'the' should be included in the english translation as it is not clear whether the sentence stops there or continues (as it would in a real life situation). E.g. Zij stierven voor de vrijheid van onze kinderen. They died for the freedom of our children.
I was assuming that the versions above were intentional and correct - that the article is used in Dutch though not in English. I am sure I have seen other examples.
What Bill says is true, 'Zij stierven voor vrijheid' is a bit strange in Dutch(though it is grammatically possible), but 'Zij stierven voor de vrijheid' is a right sentence. I understand the confusion though..