It certainly depends on what kind of group, but if it is a group with similiar interests, I would point out that the Us constiution was only signed by some hundred white men. And if we learn from that and can find more people willing to sign a constitution, then we could create a constitution to form the United States of All.
Right now we have officially regarding, WHO and Worldfoodbank, about 2 Billion people (30% of mankind) suffering from water shortage and among them 1 Billion are also starving. Every 3,6 seconds one child dies, because of this.
And this seriously could be prevented if the governments of all nation would want to stop it, but they don´t want.
As consequence there has to be a change in politic and mankind to unite in order to survive. Just imagine one big disaster like a vulcanic eruption that darkens the sun around the globe for 6 weeks, like it happened 2 centuries ago, then the global food output would shrink drastically and then much more than the 1 billion would starve to death.
This can be prevented if mankind would stop insisting on nationalism and would remember that we all are humans and should help each other.
Just see, it costs about 10 cent to keep one child one day alive. But now people in the western world say they are to poor to give $3 or 3 € per month to keep another human alive. The truth is, that actually most people simply do not want to share, because they would have to drink one beer or glas of wine less per month.
And we have to make people aware to change this attitude.