Britain's vote to leave the European Union will lead to the political end of the United Kingdom, the president of the Council on Foreign Relations told CNBC on Friday.
There will "no longer be Great Britain, at best you'll have Little Britain," Richard Haass said.
"This is Dissolution Day," he said. "This will light the fuse for Scotland, a second referendum [to leave the U.K.]. They'll opt for Europe over the U.K. I [also] worry about then what happens in Northern Ireland."
"It's easy to sound melodramatic, but the European project is three quarters of a century old, and people take its peace and prosperity for granted," said Haass.
There's too much emphasis on the negatives of the EU such as the inefficiencies and over-regulation, Haass said. "But this is playing with history, and people are going to look back on this and they're going to say, 'This was a colossal mistake.'"
The Brexit vote shows the "danger of governing by referendum," he argued. "People went to the polls without the full understanding of the consequences of what they were setting in motion."
The "knock-on effect" of other nations looking to leave the EU is "very real," Haass said. "It goes far beyond whatever gyrations happen in the market this week."
For example, he added: "You'll have people in the right in France calling for Frexit."