Time magazine (6-13 Jun 2015) asked this question of two experts and a celebrity: Zbigniew Brzenzinski, National Security Adviser in the Carter administration; Cass Sunstein, professor at Harvard Law School, and Yoko Ono.
Brzenzinski provides one forebodding scenario that might bring world peace:
Worldwide peace is most likely only some decades from now, when threats to humanity’s existence generated by global warming, pollution, etc., become an imminent threat to all.
In brief, only world peace driven by a recognition of the threat to everyone’s survival is the most likely source of salvation for a shortsighted humanity currently not able to see and think beyond the immediate.
While his assessment of humanity’s shortsightedness is certainly accurate, he gives a rather depressing photograph of possible initiators of world peace.
Sunstein gives a set of conditions that might lead to world peace:
Democracies do not generally go to war against each other: their leaders have strong incentives to maintain the peace, and information flows freely, breaking down echo chambers and enabling people to find conflict-free paths. As self-government and freedom of speech spread, world peace becomes more feasible.
However, democratizing the world has turned out to be a much bigger task than we Americans originally envisioned. Both Brzezinski and Sunstein seem to agree that world peace is possible, but it’s not going to happen in my lifetime.
Ono just wrote platitudes and contributed little to the discussion: “We are very, very close [to world peace] since we know that there is no recourse.” I consider myself an optimist, but that statement is clearly unrealistic.