Thanks ! That worked.
It takes 3 attacks to take down a Trading Post to eliminate it. Again, you reminded me, but I had already taken out the protecting fort.
So, for everyone - if there is a protecting fort next to a Trading Post, it has to be eliminated - - and the number of attacks depends on if it has troops inside or on the field, and its size - - - it would take multiple attacks to bring it down. Spy it to see how large it is, and remember to keep spying it if it gets reinforced.
Then follow by taking the Trading Post out - - - You can only build on it if you have the Trade Administration level available AND have the Trade Logistics level to establish your ownership.
Thanks again Angela.