"India", Winston Churchill observed, "is a geographical expression. It is no more a united nation than the equator." Churchill has been proved wrong. In the 50 years since it gained independence it has survived not just as one country but as a fully-fledged democracy, the world's largest.
The next 50 years of India's existence as a united country is less certain, however. A general election begins on February 22nd which may undermine the cohesiveness of the nation.
Much will depend on the performance of the Congress Party, the party of Nehru and the Gandhis, which has ruled the country for most of its independence. Congress is in decline, a terminal decline say its critics. But even its critics admit that it might yet be stabilised and strengthened if Sonia Gandhi can be persuaded to take over its leadership.
The prospect of that happening was virtually non-existent up to a month ago. Sonia abhors politics and public life. Her husband Rajiv was assassinated six years ago and her mother-in-law Indira in 1984.
In her book of photographs, Rajiv, published after his death, Sonia split their life together into two starkly contrasting halves.
Part One, The Life That Rajiv Chose, contained photographs of a happy, relaxed domestic life and Rajiv the airline pilot. Part Two, The Life That Chose Rajiv, offers photographs of a different order, Rajiv tense, under strain, overweight, swamped by crowds.
For Rajiv, though, duty came first and his mother had no one at her side that she could trust. Of his decision Sonia wrote:
"For the first time, there was tension between Rajiv and me. I fought like a tigress - for him, for us and our children, for the life we had made together . . . above all for our freedom."
His assassination confirmed her worst fears. Ever since she has rejected outright all entreaties to enter politics and assume her place in the Congress Party, the family firm.
It says something for the condition Congress is now in that Sonia should decide to campaign for the party. Spurred on, perhaps, by her politically-interested daughter Priyanka, she has finally been won over by the argument that the party faces permanent irrelevance (if not extinction) unless she plays her part.
To enter public life will put herself and her family at even greater risk. But to deny support to Congress now might put at risk all that for which her husband fought and gave his life.
Two years ago Congress suffered its worst election result. It secured only 140 of the 542 parliamentary seats compared with 198 seven years previously and 415 in 1984.
Over the last two years it has supported, brought down, supported and again brought down the fragile coalition government of the United Front; the credibility of Congress is at an all-time low. Moreover, it has a formidable rival in the Bharatiya Janata Party (BJP) which, since the last election, is the largest party in parliament.
The BJP is confident that next month's election might put it and its allies into government. Because it is on a roll, it has won over defectors from other parties (mostly Congress).
If the election result puts it and its allies close to an overall majority, there can be little doubt that further defections would follow.
The defining motif of the BJP is Hindutva or `Indianness'. It is a quasi-religious feature which implies exclusiveness rather than inclusiveness. Of more concern, party leaders have been to the fore in attempts to build Hindu temples on sacred sites occupied by Muslim mosques.
The core of the BJP is a brotherhood called the Rashtriya Swayamsevak Sangh (RSS). Formed in the 1920s, the RSS has Hindu revivalism as its core ambition and there are limits to the votes such a priority can win.
And yet the BJP widens its support partly because Hindus feel that Congress (and other parties) have gone too far in appeasing the Muslim voter, partly because of resentment among upper-caste Hindus over mandatory quotas of government jobs for the lower castes.
For the moment the BJP does not have support across the country. It is strong in the north and west, weak in the east and south, but it is busy building alliances with the increasingly strong regional parties.
In many ways the BJP has become what Congress is no longer. It is highly disciplined, unitary and centralised. It is focused and driven.
Its centralism may pose problems, given the trend in Indian politics towards fracture and greater power for the regions. Regionalisation is in vogue and if voters do not go on regional lines then, in large measure, they vote for parties standing for sectional interests, caste or a simple single issue.
BJP followers believe, however, that the voters will soon tire of weak, contradictory coalition governments and will turn instead to a party which can provide stable, strong government from the centre.
The voters may or may not seek strong, centralised government. But what is indisputable is that if Sonia cannot quickly breathe life into Congress, then the BJP might be the only party to offer it.
Reviving Congress would mean more, though, than some travelling and some speeches. For the Congress faithful, nothing will suffice other than Sonia taking over the leadership. Truly the party needs her more than she needs the party.
In the meantime the party hierarchy pleads with her to fight a seat so as to raise her profile in the campaign; three seats in Uttar Pradesh are being "kept aside" for her but she has not responded.
Sonia is at a turning point. She must decide whether or not to go the extra mile for her family's party and perhaps make sufficient of a difference to help Congress back into government in coalition with others.
Her popularity runs deep and wide. The icon of Indian politics, she is referred to as Lakshmi, the Goddess of Good Fortune. She is respected across party lines for her dignity. Her conduct is beyond reproach.
But if she commits wholeheartedly to the Congress campaign she will come under attack from the BJP for her Italian ancestry.
Thirty years in India, fluent hindi and traditional dress will not give her immunity from nationalist taunts. And neither will Congress opponents be slow to drag up the Bofors corruption allegation that plagued her husband.
Sonia married into a family that was born to rule, and the pressure must be intense. The price might be as well. As she wrote of Rajiv's entry into politics: "I was angry and resentful towards a system which, as I saw it, demanded him as a sacrificial lamb. It would crush and destroy him - of that I was certain."
The system now demands it of her.