The atrocities in Mumbai have concentrated attention on the threat of jihadi terrorism, whether home-grown or inspired or supported by Pakistan.
The weekend before the attacks, the Indian prime minister, Manmohan Singh, gave a speech at a conference of directors and inspectors general of police in which he warned against the threat of left-wing extremism in India. It was, he said, "perhaps the most serious internal security threat we face". This was a reference to the Naxalite Maoist rebel movement active in more than half the country's states, with forces of roughly 15,000-20,000 permanently armed cadres.
Named after Naxalbari, a village in West Bengal where a violent uprising took place in 1967, the various groups in the movement carry out bombings and hijackings, causing hundreds of deaths each year, and control a fifth of India's forests.
Days earlier, shock had greeted official confirmation of the discovery of the country's first Hindu terror cell, thought to be responsible for a series of bombings previously blamed on militant Muslim groups. There were links to a former student leader in the Bharatiya Janata Party (BJP), the Hindu nationalists who form the country's main opposition, and to an army colonel. This last aspect was particularly worrying, given the welcome tradition of apoliticism in the armed forces.
The month before that, Hindu right-wingers, dubbed "Saffro-Nazis", killed more than 500 Christians in Orissa, forced many others to convert and displaced tens of thousands, all supposedly in retribution for the murder of a local leader for which Maoists claimed responsibility.
India was always an unlikely nation. The British claimed only empire could keep it together; the high-ranking Raj official Sir John Strachey declared that "there is not and never was an India, or even any country of India possessing any sort of unity - physical, political, social or religious". For decades after independence its break-up was predicted. Factors such as the diversity of languages spoken (22 are officially recognised by the constitution), however, have not led to the territorial divisions some anticipated. Progress has been made in overcoming other deep clefts, as shown by the fact that a Dalit (untouchable) woman, Mayawati Kumari, is in her fourth period in office as chief minister of Uttar Pradesh, the most populous state in the country.
The real threat is not, perhaps, to the territorial integrity of India (although it is just possible that there may at some point be movement on Kashmir), but to the idea of India - that secularist, pluralist dream of Nehru and other early Congress leaders.
For since independence, as the historian Ramachandra Guha puts it, India has not become a "melting pot" but remained a "salad bowl" culture. While there has always been friction between the different constituents of that culture, the rise of the BJP, which first came to power nationally in 1996, marked a hardening of sectarianism.
"There has been an erosion of the liberal ethos in the Indian elite," says Sunil Khilnani, director of the South Asia Studies Programme at Johns Hopkins University in Washington, DC. "Twenty to 25 years ago secularism was healthier in some ways."
In spite of the recent terror attacks he, at least, remains an optimist. "I don't give up hope in moments like this. There is no alternative to the [secular, pluralist] aim that India at its best has set itself - unless the country is really going to descend into regular violence."