I seem to remember reading (In Hard Landing, I think) that AA had big expansion plans for DEN around the time Frank Lorezo was merging Texas International and Continental. CO and TI together had a pretty sizable operation at DFW, so AA and CO kind of had a gentlemen's agreement and CO stuck to HOU and DEN, while AA developed DFW and ORD.
In 1998 Continental Express wanted to fly rj's from DAL-CLE and speculation was that AA felt that CO was reneging on the gentleman's agreement. When AA launched DAL-AUS flights in August 1998, they also started some AUS-HOU-LGA trips supposedly as a warning for Continental to stay out of Love Field.
I think that was the gist of what I read in Hard Landing
The article (written in 1987) went on to say:
Speculation was that Lorenzo got to Crandall and reminded him of a few things. Things possibly like "I won't play in your back yard if you don't play in mine." American had announced big plans in the Denver market. No such plans exist today. Continental, while expanding into many back yards hasn't done so in American's two new hub operations. (At the time, DFW and ORD). If this speculation is true, you can bet it wasn't done on the telephone... (ref: the conversation between Crandall and Braniff's Lawerence that caused a major public uproar a few years prior).