Solidarity and Teamwork

I asked in another thread and on another on what psychological/sociological term for humans working together for a common goal. I found when someone mentioned on a thread and I looked it up in the other wiki, it is called Solidarity. I guess I interpret this as a group people and their neighbors working for a common goal. I am kind of amazed at people with various personalities can work together on something especially with survival. I cannot imagine getting various individuals from all backgrounds to work together on a project but how do you get those same personalities to work together?

Well, the most simple answers would be something to pull them or push them forward. Either an incentive to work together to achieve something they wouldn't be able to on their own or have them face a problem, something they'll have to work together to avoid. Either unite them with a common goal or a common foe. Of course if they already share a few things (social status, interests, etc.) the variety of goals or enemies to choose from narrows in favor of higher effectivity.