New Delhi, Aug. 5 -- It started with Instagram posts that suggested Spain's border with Morocco was opening up. Then came Facebook users tracking coast guard patrols and TikTok videos showing where to swim.

After many shares and comments, thousands of Moroccans became convinced that Europe was suddenly within reach.

Within hours, young people began heading toward the border with the Spanish territory of Ceuta in North Africa. Packed buses rolled into the neighboring Moroccan city of Fnideq. Regional trains filled up. Taxis did too.

By the time authorities reacted, some 72,000 people had reached Ceuta in just a few days, the largest migration surge between Morocco and Spain in years. More than 80 migrants died on both sides of the borde...