I disagree. In 2001, AA bought TWA for several reasons, but TATL slots/routes likely weren't among them. Ten years prior, AA had bought TWA's London routes and gained access to Heathrow, and the remaining TWA TATL routes weren't worth anything.

UA had announced a takeover of US and would have become much larger than AA, so buying TWA would have permitted AA to keep pace (had the UA purchase of US happened).

In 2000, ORD was completely maxed out and Mayor Daley was holding fast to his position that ORD did not need (and would not get) reconfigured runways. AA's plan was to route low-yield connections over STL which would permit more capacity for CHI local traffic, reducing the stress of over-crowding of T-3 and ORD in general. Following September 11, 2001, Mayor Daley reversed himself and agreed to what became the current plan of several parallel runways.

Speaking of September 11, 2001, that horrible day decimated airline revenues, temporarily eliminated overcrowding at ORD and dealt the death-knell for STL. September 11, 2001, also killed the former Reno Air network as AA cut and cut and cut to stem the cash drain in late 2001. AA tried to keep the STL hub, trimming it several times before finally shutting it down.

Buying TWA also eliminated a low-fare competitor to the Caribbean, as TWA was flying a lot of capacity to SJU and elsewhere (jetBlue would eventually replace TWA as the low-fare juggernaut to SJU).

But TATL slots? TWA was flying to LGW, but that had no value to AA. CDG? Open skies. TLV? AA told TWA to terminate that before the deal closed due to years and years of losses. CAI/RUH? I don't think that's why AA bought TWA, and in any event, that flight died on September 11, 2001. I may have overlooked one, but that's the extent of TWA's TATL operations in 2001.

What happened to TWA (and Reno) were tragic, but OBL was the reason for the demise of the STL hub and the destruction of the Reno network.