The 20th century is not my forte, so I may not be of much help in suggesting topics from that period. I know more about the 19th century but am still not an expert. Having said that, I like all three of these topics. The second may be the most difficult to pull off; as you say, it would be hard to narrow the thesis to something manageable.
For projects like this it’s always best to restrict the potential amount of material you’ll have to sift through. The language issue is also important for certain topics, although if you are Danish you’re probably a lot better off in that area than most English-only Americans.
I would say that if these topics interest you equally or nearly so, go with the one that has the most manageable bibliography and will be the least likely to arouse the animosity of your committee. Your bachelor’s thesis is not your “95 Theses” to nail to the door of the university. It’s to prove you know what you’re doing as a young historian so that graduate schools will consider your application seriously (if your goal is in fact to go on to graduate school).