I've written up some ideas on how to incorporate political / military alliances into KM2e.
https://fcain.tripod.com/pf2/kb_ally.html
Given PF2's stance on having only three types of bonus (circumstance, item, and status), I've decided that this bonus makes most sense to me as an Item Bonus, given how much effort (four turns, or more) will be needed to make an alliance.
I'd appreciate your thoughts.
Thanks,
Franklin
Benefits of an Alliance
When two kingdoms join together in an alliance, each kingdom gains an item bonus (equal to the rating of the alliance), to be used used on all (appropriate) checks of Boating, Engineering, Politics/Statecraft, Trade, and Warfare, made with their ally. This level (and item bonus) starts off at the minimum of +1, and can be improved to as high as +3.
Allied kingdoms can make improvements in each other's territory. Regardless of who actually paid for and built the improvement, the kingdom who owns the hex is the one who officially owns (and benefits from) the improvement.
Allied kingdoms can move their armies into and through each other's territories, and can station them in each other's territories or in unoccupied fortifications, although not inside allied settlements. If an allied kingdom deploys an army into your territory, you must succeed at a Politics check, or else gain 1 Unrest. (However, this does not apply if your kingdom has been attacked and you have requested aid from the ally.)
If you are attacked by another kingdom, or suffer some other calamity (such as a randomly rolled Event), you can call for aid from your allies. The precise nature and amount of aid that your ally sends to you is at the discretion of the ruler of the ally kingdom. (Speaking "out of character," it will be up to the GM to decide what aid, if any, is sent to you.)
Likewise, if your ally is attacked or suffers some other calamity, you can expect to receive a request from your ally for aid. If you fail to send an apprpriate amount of aid, and in a timely fashion (GM's descretion as to either case), the GM will determine what backlash (if any) occurs.
In the event that an alliance is lost, should you have any armies stationed in that former ally's territory, you must deploy them out of that kingdom the very next turn, or else you risk a declaration of war.
Check for Backlash (Inadequate Support to Ally)
Roll a test of Politics, against the higher of either your kingdom's Control DC or else the ally kingdom's Control DC. Increase the DC of this check by +2 for each previous incident of inadequate support to this specific ally, and by +1 for each incident of inadequate support to any other ally.
Critical Success: You escape this incident without embarrassment.
Success: Gain 1 Unrest. Your alliance with this kingdom decreases by one level. If this should reduce your alliance with this kingdom below +1, then this alliance ends, and you gain 1 additional Unrest.
Failure: Gain 1d2+1 Unrest. Your alliance with this kingdom decreases by two levels. If this should reduce your alliance with this kingdom below +1, then this alliance ends, and your gain of Unrest is doubled.
Critical Failure: Gain 2d3 Unrest. Gain 1d2 Ruin of your choice. Not only do you lose your alliance with this kingdom, you also lose your diplomatic relations with them (along with any trade agreement). Furthermore, your callousness causes you to lose one level in each other alliance you may have. Any such alliance which is reduced below +1 is dissolved.
