It's not all that easy, don't forget you also have to take Spy, Reconnaissance and Surveillance cards into account. And, in team games, which territories the teammates reveal to each other (not just by touching territories, but also with *their* cards).
There is indeed already a UserVoice for this, feel free to [give it some votes](
http://warlight.uservoice.com/forums/77051-warlight-features/suggestions/1920689-partial-history-see-what-only-one-player-could-s).