AHMEDABAD, India — India’s most important election in a generation began in earnest this month the same way consequential elections nearly always start here — with a proclamation and a deadly riot.

In New Delhi, the Bharatiya Janata Party announced last week that it had chosen Narendra Modi, one of the most divisive politicians in India’s history, as its candidate for prime minister in next spring’s national elections. Mr. Modi, the chief minister of the western state of Gujarat, is an unapologetic Hindu chauvinist who has been accused of mass murder.

Mr. Modi has tempered his anti-Muslim tirades and replaced them with a message of development based on a record in Gujarat that even critics acknowledge is impressive. But critics also say he and his Hindu nationalist party have benefited from past violence between Hindus and Muslims, using it to paper over Hindus’ historic differences over caste and get them to vote as a bloc along religious lines.

Not coincidentally, mass rioting broke out last week in Uttar Pradesh, India’s most populous and politically important state, after a legislator from Mr. Modi’s party circulated a fake video of two Hindus being lynched by a Muslim mob. Forty-four people were killed and 42,000 were displaced as villages were sacked.