While previous general elections in India have been fought over national issues, this time around coalition mathematics seems more important than campaigns over economic growth, terrorism or inflation.

With both the major national parties, the Congress and the Hindu nationalist Bharatiya Janata Party (BJP), being shunned by their regional allies across the country, the likelihood of a coalition of disparate parties coming to power after the April-May general elections looms large.

Not that India is new to coalitions. The Congress has ruled for most of the last five years through a stable coalition, the United Progressive Alliance (UPA). So did the BJP before that between 1999 and 2004 with its National Democratic Alliance (NDA).

The worry is that a coalition without a strong Congress or BJP to lead and hold it together will not last the full five-year term. It happened in 1996 when 13 parties came together to rule and fell two years, and two prime ministers, later.

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It was not always like this. The Congress, which led India's freedom struggle, won the absolute majority of votes for decades after independence in 1947 - somewhat akin to the African National Congress's hold over politics in post-apartheid South Africa.

But a gradual erosion of support for the Congress, beginning in the mid-1970s, saw mainly national opposition parties, including the BJP, make steady gains and come to power in the 1990s.

And now in 2009, it may be the turn of regional parties who have already tasted power in the states, to come together and rule the country.

This motley group is called the Third Front and they have positioned themselves as the alternative to the UPA and NDA.

For their detractors, the Third Front is just an umbrella that could be folded away for parties that are not with the main coalitions.