From the article: > a market opportunity for games that combined elements of tower defense games like Kingdom Rush with the depth of real-time strategy games l

From the article: > a market opportunity for games that combined elements of tower defense games like Kingdom Rush with the depth of real-time strategy games like Star[c]raft Ironically, the first tower defense games were custom maps in Starcraft. I probably still have my copy of the Art of Defense on a backup drive...