It took longer than I thought. Learned something new again. To be honest, I didn't think this way of playing was possible. My result is still quite modest. You can get much higher score. Probably I won't try it again (it kept me busy all day today). It is possible to spam the whole map with trade districts and maybe only leave single territories with AI to trade with them etc. It was fun in any case :D

The exact result is: 2088397

Save file:

Indians Turn 75 paxis76.ctr