I'd say their peak started in the 40's and ended in the early 80's. TWA, along with Pan Am, was the flagship for international air service.
I can remember a "snack" flight in coach yielded a small steak and onion rings! First class service was downright hedonistic. Pleasant, engaging, and sycophantic flight attendants catered to your every whim. All food was served off a trolley, and all items were served and retrieved with silver trays!.....in short an era "gone with the wind" and never to return.
Where did they go? Most major cities in the U.S. and and practically all in Europe. Cairo, Riyad, and Tel Aviv to boot. Heathrow alone was served from JFK, LAX, BOS, STL, and OHR!
It's a sad ending for TWA given its past.
Oh, for the good old days....