India, Dec. 7 -- A few years ago, when ShashiTharoor stood at Oxford and argued that Britain owed a moral debt to India and its former colonies, his words were treated as an eloquent aside rather than a rallying cry. He suggested that even a simple apology would signal remorse for centuries of plunder and subjugation. At the time, he was largely a solitary voice. That is no longer the case. What was once an academic argument has now consolidated into the largest global demand for reparations in recorded history?

In an extraordinary development, former colonies of the British Empire have jointly advanced claims amounting to an estimated $180 trillion. This unprecedented figure transforms decades of moral debate into a concrete economic re...