When people come together, it can be powerful, but there are many ways to describe this unity, beyond the phrase "bands together". You might describe a group of people as "united", "joined forces", "merged", "combined" or "coalesced". If they're working together to fight a common enemy, you could say they're "allied", "identifying", "joining hands" or "forming a front". Sometimes people band together to lend support, in this case, you could say they're "coming alongside", "banding around", "coming together", or "standing together". Whatever phrase you use, the important thing is that the group is working in concert to reach a common goal.