Civilization – Do you gain war weariness when your cities participate in combat

I noticed that I broke my promise after one of the forward-settled cities of the Aztecs failed to withstand the passive religious spread by close cities.

In my case the Aztec city did show the symbol of my own religion when I got the message about the broke promise, but this might just have happend by chance at the same time.

Since the game has just been released I can't be 100% sure but it definitely seems like passive spread CAN break the promise. (I'm not sure either if this is on purpose by the game developers since the player can't really controll passive spread)

There's no upper limit on the number of cities you can have in Civ VI. However, your Amenities gained from Luxury Resources can only give a bonus to four cities (six for Aztecs), so every city created beyond the fourth will reduce the Amenities available in each city. Since Amenities impact how productive your cities are you'll want to avoid expanding too fast if the Amenities in your cities are already fairly low.

Other than concerns about Amenities though there really isn't much of a negative to founding more cities, and you'll usually get some benefit from every city you create.