I know there are one or two raider features of “bigger armies of other lords attacking your territory if you don’t pay them tribute”. And while that is neat, it would neat if the player had access to a diplomacy feature that allows them to make both allies and enemies “off-map” with other cities/nations.
For instance, imagine you send an envoy to a different city. You invest into improving your diplomatic standing. You relations get better, they offer you new trade routes. Then you get a warning from another lord that sets you an ultimatum for tribute or invasion. Now you have the option to send another envoy to your allied settlement for military aid (can be weapon delivery, temporary troops, etc.). Depending on your relationship, they may even decline aiding you.
You can also make more enemies, which means alongside bandit invasions your risk of a Lords invasion is also higher, the more hostile the relations are.
Would add more depth to each map imo.