Especially if you want to make RTS games, you should definitely learn Advanced Squad Leader. Avalon Hill's games that led to ASL, and ASL, should be the game design bible of RTS designers (Panzerblitz is one of the most historically important games in the history of game design, and was the first step towards ASL). There is a whole lot in ASL that could vastly improve the RTS genre. To truly learn ASL well, and really understand it, is going to take at least a year or so of studying it and playing it. Especially if you have never played an Avalon Hill game before.
Territories is sort of the next evolution of how Avalon Hill and Amarillo Design Bureau games worked. It is fairly easily explained too people who are familiar with SFB and the impulse chart, but it really takes of a lot of explaining too those who are not familiar with SVC's games. It is not anything like modern games because it runs on a "next generation" "treadmill of time" that is the next step forward beyond SFB's impulse chart. The impulse chart was, itself, the next step beyond Avalon Hill's phased turns.
Larry Harris's War Room is just running on Avalon Hill's phased turns, but it is the first game I have ever seen that is heading in the same direction as my games. It is conceptually very similar to Territories, a simple iconic representation game like Axis & Allies or a Sid Meier game, disguising and simplifying Avalon Hill/ADB inspired rules. In this regard, they are very similar. In other ways they are very different in a lot of ways as well.