For much of the past century, the Dalai Lama has been the living embodiment of Tibet’s struggle for greater freedoms under Chinese Communist Party rule, sustaining the cause from exile even as an increasingly powerful Beijing has become ever more assertive in suppressing it. As his 90th birthday approaches this Sunday, the spiritual leader for millions of followers of Tibetan Buddhism worldwide is bracing for a final showdown with Beijing: the battle over who will control his reincarnation. On Wednesday, the Dalai Lama announced that he will have a successor after his death, and that his office will have the...