The situation at ORD today is very similar to DFW in 2005. I remember at the time, people thought DFW would always have two mega carriers, AA and DL going head to head forever. The thing is, having a duopoly with two mega carriers going head to head so fiercely is completely unsustainable in the long term. ORD is the last remaining example of such a duopoly at a single airport in this country for a reason- all the other ones have slowly been lost to the stronger airline when the other decides to take it easy. Within a couple year's time, I would be willing to bet that UA edges out AA to the point where AA will find it harder to keep up if they don't change their strategy and make ORD a priority. The only reason that ORD is a hub for AA is because it is profitable. If UA cranks up the heat and turns the cash flow in the other direction, AA may seriously take a long and hard look at their commitment to ORD, how AA slowly pushed DL out of the market by making DFW unprofitable.
ORD is UA's #1 hub
ORD is AA's #3 hub
You tell me who's more determined to take control. As someone mentioned above, UA doesn't have a dominant airport with 700+ flights, and they have more incentive to kick out AA. ORD may have two carriers today, but so did DFW not that long ago. I really don't know if ORD will be able to keep both forever. I hate to portray such a negative outlook, but it's a reality that most won't understand until it's here. 10 years down the road, we may find it hard to believe that there was actually a time that AA had a hub at ORD the same way many find it hard to believe today that DL actually ran a big operation in DFW as recently as 2005.
Huge, huge differences between AA at ORD in 2017 and DL at DFW leading up to 2005.
DL built up a DFW hub in the 1980's after the demise of Braniff. American had, in the late 1970's, moved its HQ from NYC to DFW and it was always clear that American would be #1 at DFW. It gained the most number of gates and terminals and was the only true airline that added long-haul destinations to markets where there was significant O&D to North Texas (NRT, LGW, FRA, CDG) and tried a few others such as BRU and MAD.
DL, conversely, set-up DFW simply as a strategic South-Central hub that would provide relief over Atlanta, and also connect the DL network to secondary and tertiary markets in the Southeast, Southwest and Central Plains. DL never had more than one international long-haul route from Dallas (FRA) which wasn't even an organic DL route: it was an authority acquired from Pan Am. This was also pre-consolidation, so it was a bit more normal to see airlines have secondary hubs and focus cities in certain markets that were already crowded (read: CO at DEN, HP at LAS, US at BWI, AA at BOS, etc).
Over the years, DL was vocal about how challenging it was to make DFW work because it simply did not have the size, scale, and resources to compete against AA. Any efforts to make that would have required diverting attention away from ATL, which was (and still is) massively profitable for the carrier. The economic malaise of the late 1990's and early 2000s made it almost impossible for DL to make money at DFW. DL couldn't run more than 2-3 daily mainline flights to a market like LGA or DCA, for example, based on the number of gates and aircraft that it had, as opposed to American which could run hourly shuttles.
Over the years, DL converted DFW to a mostly regional hub sans for core markets like SAN, SFO, SEA, BOS, LAX, FLL, MCO and the main hubs, but the oil spike above $50/barrel made it even more challenging to make money on such high-CASM regional aircraft. Plus, who really wanted to fly 4 hours on an RJ from DFW to JFK or OAK when you could get mainline on AA?
In the final 12 years leading up to the eventual de-hubbing of DFW, Delta admitted that DFW had only been profitable for 3 of them. And DL was also headed for Chapter 11. It made zero sense to keep open the DFW hub, as sad as it was.
American is in the best financial shape that it has ever been in history.
ORD for AA is nowhere near the same situation. AA may have more regional flights on a daily basis than mainline, but largely these are to core/unique markets in the Upper Midwest, Central Plains and Southeast where AA can command a fare premium. Among the largest GDP/metro areas in the U.S., AA flies mainline to virtually all of them. Heck, even medium-sized cities like PIT, JAX, RNO, SMF, SLC and ORF are seeing mainline on AA from ORD these days.
Plus, international at ORD is not insignificant. You have multi-daily to LHR, plus NRT, PEK, PVG, CUN, YYZ, YUL. You have seasonal to MAN, MBJ, CDG, PVR, PUJ, FCO, SJD, CZM, DUB, GUA, VCE.
DL at DFW did not have any of that.
One final thing worth mentioning is how much AA is ramping up their Corporate Sales channels, tools and personnel to the extent that it will be fiercely focused in a market like Chicago.