There are 4 main arenas, early war, mid war, and 2 late war. In each arena, there are 3 countries Knights, Rooks, and Bishops. I'm not sure of the years, but early war is planes in early 40's, Mid is mid40's, and Late, late 40's. You can fly spits against mustang and such, but that alone adds another demension to the game due to all the "what if this happened in WWII?"
Combat Tour is going to be a timeline bases set-up were you will start a "character" and by joining mission and performing the objectives of those missions will move you up in rank. Check under the Combat Tour part of the forum for more info.