if theres one thing i noticed in all apps thats uses the kingdom vs kingdom an then the guild vs guild setting, is that there are no guild alliance option; the feature or option to ally your guild with another guild, paving the way to greater wars between other guilds.
The only online game that does have this feature is EVE Online (guilds joining together to create a mega guild or alliance of guilds, in eve online's case an alliance of corporations formed into one large mega corporation - yes i've played it, just don't have the money an the comp that could play it is dead), so why not use that as a suggestion?

Sooner or later, there will be several or more guilds that will reach a high enough level (with their players also at high levels) where they'll be bouncing back & forth between guild levels (one guild wins, they gain exp, while the loser loses exp), somewhere along the way those guilds will make secret alliances that other guilds will not be aware of an will enter a world of hurt if they step on the wrong toes. Then the obvious bullying will come around an then the devs will bring in the different realms that most apps use. So to eliminate the need for that, lets make it possible for guilds to ally with each other to create mega guilds with their own respective levels with 5 to 10 guild max allies (guilds not guild members), an instead of adding the entire list of members to the roster of the mega guild, just add the leaders along with their 3 highest ranked members (that the leader ranked), every guild that is allied with each other will be able to see which guild they are allied with an so will anyone that checks them out.

This suggestion is not only meant to suggest a mere option of allying with other guilds, but to create greater challenges, rewards, bonuses, an wars.
Also in another suggestion, I mentioned a warehouse an a trading/reinforce feature, with that in mind, if other guilds were to ally with each other, a mega guild warehouse would be available that can only be accessed by the guild leaders an to eliminate the "snatch, go, an unally" (a possible exploit that would severely anger people), just add a lil permission option (This "player name" can take this "item/troop icon" or anyone can take item/troop options).

Please give your honest opinions of this suggestion, further thoughts on this might be needed (just a thought).