Limit PvP dogpiling

Question

Browser-based strategy game where you play an empire vs other player empires. The main PvP element is battles between empires where outcome results in gaining or losing rank. Troops are also damaged/lost in battles.

You can only declare war (enables battles) against empires of a similar rank. War then remains active until one side surrenders, lost too many battles or there was no battles for x amount of time. This works fine as far as making any single war reasonably balanced at the time it starts. Wars are 1 on 1 but you can be involved in several simultaneously effectively making 1 vs many possible.

I would like diplomacy and alliances to be a part of the game, but I also want to prevent excessive dogpiling. The difficulty here is finding a working middle road between:

A. No simultaneous wars (if someone is already at war you cannot attack). This results in "phony wars" as players go to war just to prevent anyone else from attacking them while building up for a real one.

B. No attack restrictions which easily results in everyone within rank range jumping some poor guy and wrecking him.

Some mechanics I already have related to this are:

• For each war you have a stance for your troops ranging between Defensive-Offensive. Offensives will tax your economy more but is needed to push for a conclusive victory.
• Defenders advantage applies when fighting defensively inside your own territory.
• Less gains from winning against lower ranks which comes into play for many vs 1 wars when the 1 starts losing rank from surrenders/lost battles.

This makes dogpiling less profitable, could even be a net economic loss for most winners. Doesn't matter though, players still do it.

I'm fine with many vs 1 wars sometimes happening, the challenge is to have it be the exception rather than the norm. My current line of thought is to not limit the option of doing it but to keep tacking on more penalties until it gets to an acceptable level. What I'm looking for with this question is examples of rank-based systems which achieved this already and/or suggestions of new mechanics that would take my game in this direction.

Answer 1

When you don't want players to do something, don't give them an incentive to do it. When it is neither damaging for the victim nor an advantage for the attackers, then there is no point in doing it at all and players won't bother to organize it.

Consider to not have any penalty at all for losing a defensive war (including not losing any units or other resources). So only the attacker is at risk of losing their score and resources when they start a war. That way dogpiling will be a victimless crime.

You could also make it a pointless crime. Limit the amount of resources which can be won by attacking a given player in a given timeframe. So when 10 players gang up on one target at the same time, each one only gets 10% of the usual reward at most (score and resources). This, however, opens up a new exploit: starting phony wars to reduce the reward of the "real" attackers.

Answer 2

One way to limit the phony war exploit of Philipp's answer would be to have a rule of transitive agression.

A is at war with B

A is not an ally of C

C attacks B

C is now at war with both A and B

Effectively if someone decides to dogpile, they have to fight everyone, not just their intended target.

Coupling that with Philipp's suggestion of "divide the spoils among the allies" your player choice is to either fight everyone by yourself, and keep all the reward for yourself; or pick a side and split the reward with your allies.