Is interpretation of known historical facts protectable under copyright law?

Copyright law is relatively simple to understand - you simply cannot COPY someone else's work. And yes, your own work is then copyrightable. Your work can effectively be the same as someone else's work - as long as you didn't actually copy it. So, for example, let's say you did research on WW II, analyzed all of the major battles by all of the major players - Germany attacks Poland, Germany takes over and occupies France, Germany then turns its attention to the Soviet Union, whatever - you can write your own analysis as you see it, as you have interpreted it, reach your own conclusions as to why the Allies won the war and why Germany lost the war - as long you do not COPY anything from anyone else. That is basic copyright law.