Five hundred years ago, Guru Nanak founded the Sikh faith in India. The Sikhs defied the caste system; rejected the authority of Hindu priests; forbade magic and idolatry; and promoted the equality of men and women -- beliefs that incurred the wrath of both Hindus and Muslims. In the centuries that followed, three of Nanak's nine successors met violent ends, and his people continued to battle hostile regimes. The conflict has raged into our own time: in 1984 the Golden Temple of Amritsar -- the holy shrine of the Sikhs--was destroyed by the Indian Army. In retaliation, Sikh bodyguards...