I have an idea (might be mentioned before, i dont know)

Why is diplo not a setting? (with different subsettings)

If diplo is on:
You can not attack a player you have not declared war on (to declare war: click on the player name and click "declare war"), this could be optional
other options are "propose alliance", which would make the two players seem like a team.
Maybe including a separate chat if 3 players are alliance with all, or a option to propose an alliance with multiple members (which all have to accept)

Ofcourse also the option break the alliance and to propose peace.

This would require quite a lot of programming ofcourse.
The whole idea should be thaught about a little more ofcourse about the settings.

this. is. like. the. thirtieth. fucking. diplo. thread. in. a. week.