I enjoy reading military history and I play war games because of the strategy involved. That said, I would never want for war to happen in real life unless it’s a just war, all in conformity with Catholic teaching. Is it a sin or imperfection for me to be fascinated with war, nevertheless, even if for academic and recreational reasons that have no serious impact on how I live my life?
In my opinion, no, it is not a sin. Being interested in history, strategy, and political dynamics is not a sin.
As you point out, truly rooting for war is what would be sinful.