This week, in India and in Pakistan, celebration and mourning are entwined. While the nations celebrate their independence from British colonialism and remarkable economic progress, they also remember the millions displaced and killed during the separation of Hindu majority India and Muslim dominated Pakistan. The 70th anniversary of partition should remind today’s leaders how divisive rhetoric can take on a life of its own, with catastrophic consequences.

When the British lawyer Sir Cyril Radcliffe finished laying out a boundary between the new nations, millions found themselves on the wrong side of a hastily drawn line. A weary Britain beat an irresponsibly hasty retreat and by the end of the mass migration of Hindu and Muslims, more than 15m people had been uprooted. More than a million had lost their lives. Pillage, rape and murder accompanied the birth of both nations, and partition sowed the seeds for three wars the two have since fought over contested lands.

It did not have to unfold as it did. While British policy had encouraged religious divisions, key leaders such as Muhammad Ali Jinnah and Mahatma Gandhi — remembered today as founding fathers of Pakistan and India — did not at first regard partition as inevitable. Far less did they envision a religiously charged stand-off between nuclear neighbours, with the threat of war ever-present.