Lecture halls at Canadian and American universities have become battlegrounds for critics and defenders of Hindu nationalism, punctuated by threats of violence and even death.

Temples of Sikhs and Hindus in Canada and Australia have been defaced with slogans harking back to India’s timeless divisions.

Parades in two North American cities have featured displays celebrating episodes of brutal sectarian violence in India.

Mr. Modi’s Hindu-first policies and increasing intolerance of scrutiny have spilled over into Indian communities worldwide, intensifying historical divisions among Hindus, Muslims, Sikhs and different castes.

Mr. Modi’s government has adopted laws and policies discriminating against religious minorities as some of his supporters have carried out killings and acts of violence against them, often with impunity.

“What they do have is a common agenda which is to crack down on all dissent,” Ms. Kasturi said. “So any critique of Hindutva is called Hinduphobia. Any critique of Mr. Modi is called Hinduphobia.”

Mr. Modi has tapped into a “very deep-seated psychology” among members of the diaspora who “want to recover a lost pride in the rise of a great civilization that has been wronged” through colonization, said Meera Nanda, an Indian historian researching the impact of Hindutva in the United States.

“No one ever bothered about so-called Hindu identity before” in Canada, Mr. Jangam said of the years before Mr. Modi’s rise to power. “It’s a shock for me how people have transitioned from being normal, ordinary people into Hindu fundamentalists.”

In Brampton, the Indian government has also been accused of directly interfering to defend Mr. Modi’s policies or India’s image in ways that have deepened divisions.

In 2017, Indian diplomats from the consulate general in Toronto pressed organizers of an annual cultural festival to cancel a pavilion devoted to Punjab, the only Indian state where Sikhs are a majority, or to fold it into the India pavilion, according to Brampton city staffers at the time.

“The organizers shared with us how they were getting phone calls and they were being harassed by the Indian consulate to shut this pavilion down,” said Jaskaran Sandhu, an adviser to the mayor at the time.

The Overseas Friends of the B.J.P., the international arm of Mr. Modi’s party, has established a growing presence abroad to push its agenda, and is registered as a foreign agent in the United States.

In Canada, which does not have a foreign agent registry, the Overseas Friends of the B.J.P. of Canada was established in 2014 and changed its name to the Canada India Global Forum in 2018.