Bill Clinton has warned that some Brexit voters may only now be realising the impact of their decision.
The former US president said the choice between community and tribe will determine how the world meets the threat posed by climate change, inequality and other great challenges.
After being honoured by Dublin City University for his work on peace and reconciliation in Northern Ireland, Mr Clinton said he used the example of the Good Friday Agreement shamelessly around the world.
But he warned that the Brexit vote was about people thinking differences are more important that what they have in common.
“Now, there are lots of people who think they are less human,” he said.
(Niall Carson/PA)
“Now given the economic inequalities and the rapid pace of social change and all the upheaval that’s going on …. people are reassessing whether what we have in common is more important than our differences.
“A lot of people begged to differ.
“That’s really what the Brexit vote is all about.”
Mr Clinton was awarded an honorary doctorate of philosophy, DCU’s highest honour.
Alongside him were Sister Stanislaus Kennedy, a lifelong social justice campaigner who founded Focus Ireland, the country’s biggest homeless charity, and the Immigrant Council of Ireland.
Also honoured at the event in the Helix was Martin Naughton, founder of manufacturing giant Glen Dimplex.
Mr Clinton reflected on his own legacy with the Good Friday Agreement, signed in Belfast in 1998, mid-way through his two terms in the White House.
Ultimately the accord was brokered after he took a more hands-on approach to US diplomacy on the island of Ireland at the height of the Troubles.
Mr Clinton travelled direct to Northern Ireland for private meetings with politicians after the ceremony – his intervention in the political stalemate delayed by a day because of Storm Ophelia.
In a lengthy address to hundreds of invited guests and students in the Helix in DCU, Mr Clinton warned about inequalities and divisions.
“The world is now in a conflict whether we should stop our mingling with others at the tribal level or whether communities are better; whether diverse groups make better decisions and create wealth and life and opportunity or homogenous ones do as they don’t push us so hard and we feel more secure,” he said.
“We can’t get away from each other so we should look at our neighbours without regard to their race, religion, their orientation or whatever.”
Mr Clinton raised concerns about the rise of nationalist parties in Germany, France, the Netherlands and Austria and also the impact of Brexit.
Mr Clinton added: “All partnerships that are community-based are held together not because everybody agrees with everybody else, not because we don’t still have our particular identities, but because co-operation is better than conflict or isolation in any environment in which you must be in touch with others.
“It’s a simple proposition. But we are re-litigating it now.”