The history of nations is one long shifting of alliances. If we're stronger as a group than we are individually, then several groups working together are more powerful still. This is the reason that great leaders throughout history have sought to unite the tribes. Sometimes this was accomplished at the tip of a sword. Just as often, however, tribes came together of their own accord, if not out of friendship than at least driven by mutual need.
There are a great many benefits to alliances. You have the combined talents of a diverse group and that many more arms and legs working towards a common goal. You also have the strategic thinking of the combined group, which will often see beyond your personal blind spots.
When you're building relationships, networking with like minded people is always a good place to start. Even so, don't overlook those who have completely different talents and perspectives. You'll often find that you're stronger by joining forces with a diverse collection of people due to the many additional capabilities you gain.
You should always approach things from the perspective of the other group's benefit, not your own, if you want to get their attention. Having done that, you should then be sure to let them know your own motives for the alliance.
Most people will raise an eyebrow when hearing from those who offer help seeking nothing in return. While there are altruistic souls out there who would do just that, your potential allies have lived long enough to know that everyone has an agenda. If you don't make yours plain, they'll be suspicious of your motives. When there's something in it for everyone, however, the power of joined forces is a significant tactical advantage.