When the states of what would be independent India were drawn up in the dying days of the British Raj, the criterion used was linguistic: people who mostly spoke the same language were brought together in one state. This principle ignored minority languages and dialects within these areas, as it glossed over the fact that several north Indian states were all predominantly Hindi-speaking.

Demands for regional autonomy or separate statehood began to be raised fairly quickly in different parts of India. Among the first was the demand for a separate state of Telangana, which had been merged with other Telugu-speaking regions to create the state of Andhra Pradesh, despite local opposition. The States Reorganisation Commission of 1954 did not recommend the merger, especially as the area was just emerging from the Communist party-led Telangana uprising, a moment that is still regarded as an inspirational struggle for the left movement in India. But the merger went through, with some supposed safeguards, even though the then prime minister, Jawaharlal Nehru, said this particular marriage should contain provisions for divorce.

The concerns of the people of Telangana were mainly economic, including the distribution of resources – such as river water, as the headwaters of the Krishna and Godavari rivers were in Telangana but the planned irrigation projects at coastal Andhra. There were worries that, because this region was less progressive with lower levels of education, those from other parts of the state would take the desirable jobs and become the ruling elite, and that the fiscal revenues would be disproportionately given to other areas.

Some of these concerns have indeed been justified, but Telangana is by no means the part of the state that is struggling most – that dubious privilege rests with the Rayalaseema region and some northern districts. The state capital, Hyderabad, which is emerging as a major modern metropolis, lies squarely within the region. While it is true that locals have fewer of the coveted jobs in Hyderabad, in most other respects it is hard to make much of a case for economic discrimination of the region.

But the sense of injustice has remained to some extent, and has been periodically fed by political forces. The Telangana Rashtra Samithi party was formed in 2001 when some leaders split from the Telugu Desam party to focus on this one demand. Since then the TRS has been in alliance with the Congress party at a national level, and Congress in turn has blown hot and cold on this issue. The first United Progressive Alliance (UPA) government promised Telangana statehood but did not deliver. Many hunger strikes and riots later, it seemed that this on-again-off-again state of affairs would continue, possibly indefinitely.

What changed was not on the ground, but political calculation within Congress. The party dominated the last Lok Sabha (lower house) elections in Andhra Pradesh, which in turn contributed a precious 35 seats for the ruling coalition. But when the charismatic but corrupt local leader YS Rajasekhara Reddy died in a helicopter crash in 2009, the Congress party suddenly realised that it had created too powerful a regional governor and so came down heavily on his son and heir, who is now in prison on a corruption charge despite the huge following he has massed in much of the state. There are indications that Congress may be wiped out in the state in the next general elections, which are likely to be held around next April. So this could be a last-ditch attempt to win itself some votes at least in one region of the state, while throwing the other parties into confusion and perhaps gaining from that disarray.

This petty political calculation is obviously not explicitly stated: instead, the official talk is about the genuine grievances and concerns of the people of Telangana. But already the decision – which will take around six months to implement – has generated significant side effects nationally. Regional separatists across the country have upped their antes: demands for separate states such as Gorkhaland in northern West Bengal, Bodoland in Assam and Vidarbha in Maharashtra, are getting louder and more insistent. There is even a demand that the huge state of Uttar Pradesh should be broken up into four states. India may be in for a period of enhanced instability on that score.

Some argue that this is fine, because smaller states are easy to govern. And there may well be a case for another State Reorganisation Commission to look into all of these issues. But the recent history of newly formed states such as Jharkhand does not suggest that things are always better in smaller states. What is clear is that the Congress party, in its push for some immediate political benefit, has let the genie out of the bottle – with very uncertain consequences. Once again, we are reminded that we need to be careful what we wish for.