It is called a "guild", have you ever heard about such thing? =)
Yes, I know about guilds. I know about the guild recruiters going off and desperately trying to grab more people and shove them into a guild, I know about the guild leaders that enforce mindless rules , upon their minions, I know about the guild members who only join the guild to get the free stuff and who have no intention of attending the meet-ups.
People just do not work together. Personal glory and greed are the only factors that have any effect on what a player might do, so unless you can manage to convince them that working together is the best course of action for fulfilling both those needs (and rousing speeches will never suffice, only cold programming that gives benefits for working together), you're going to have a rather spread-out army that's going in different directions.
The most spectacular show of teamwork I ever read about was the assault on Caiger Mall in the browser-based game "Urban Dead". That happened once, and there are suspicions that some people used multiple accounts to get the number of combatants up.
The most spectacular show of teamwork I ever witnessed personally was when that guy in Battlefield 2 actually agreed to follow me.