How do you prevent, mitigate, balance, and/or resolve population imbalances in games with persistent team-based PvP?
Examples of what this is not: FPS or MOBA games where one team is way better than the other; temporary imbalances caused by uneven numbers of players in small proportions; PvE class imbalance. Let’s take some examples of population imbalance. Please fix one or all of them in the comments.
Assume that factions are balanced or symmetrical (or else we have a different problem) and that most players will not intentionally self-select to a losing team instead of the winning team (empirical). The problem we are trying to solve here is the spread of the population, which is mostly a matter of quantity but may involve quality, although there is no a priori reason why the pros would join one faction and the scrubs another.
Assume also that population imbalance is a problem, particularly for the survival of the game. Sheep leave if they are just being fed to wolves, wolves leave if there are no sheep.
In Dark Age of Camelot, there are three factions on each server and multiple servers. You cannot play for multiple factions on the same server, but you can across servers. The population imbalance problem comes when one faction on a server pulls ahead. Players are more likely to leave a losing faction/server and join a winning faction/server, so victory tends to snowball over time. It is not necessarily the same faction winning on each server, so Server A might be Albion-dominated while Server B is Hibernia-dominated. Mitigation measures already in place: “Darkness Falls” is valuable PvE content open only to the winning team, which both then draws PvE players into PvP for the losing factions while draining them from the winning faction; “relics” are useful buffs that factions can capture from each other, but your faction must own its own buff to capture others’, which reduces the incentive to pick on the weakest faction because #2 cannot afford to fight both #1 and #3 (although #1 and #2 may trade #3’s relic back and forth, they are at least doing so with war in their territories, not stomping back and forth across Poland in WW2).
In Guild Wars 2, each entire server is on the same team, but servers have vastly varying populations. Mitigation measure already in place: servers are grouped to fight against similarly sized servers. As discussed elsewhere, this rarely leads to even three-way matchups because the servers would need to be in neat triples of similar population sizes (AAA, BBB, CCC) or else one server will have an easy victory or certain loss or both (AAB, BCC, CDE). Players can switch servers, the effects of which are significantly mitigated by the changing matchups based on server wins and losses; rising in the ranks means fighting similarly full servers, and changing the order or size distribution of servers only has a big impact on the overall picture if it evens out the tiers. Mitigation measure already in place: there is a cap on how many players can be on a particular WvW map, so there is a limit on how much force you can bring to bear even with a huge server.
In Shadowbane, PvP was a free for all with one server and no predefined factions. Players defined their own factions. As one group of players became the bully on the block, players either joined or left. As the sheep population falls, repeat with the smaller wolves and so on. Until one faction wins and servers shut down. Whatever mitigation measures that were tried failed, although EVE Online does very well with a similar structure. One EVE mitigation measure is the huge size of 0.0 space: no matter how big a bully you are, you cannot take and hold half the galaxy unless a similar proportion of the playerbase is in your faction.
In Ingress, there are two factions and one server. That’s about all I have for problem specification there, beyond the initial assumptions. I know of no mitigation measures, and population flows about as you would expect when one faction has more players. Exacerbation measure: players are frequently encouraged to invite their friends, and the game was invitation-only for a while, so the larger faction both had more players and had more ability to attract new players.