The World Bank has prevented money being used on arms

The phrase "power comes from the east'' has become virtually a national motto in Chad following Idriss Deby's Sudan-backed overthrow of previous Chadian head of state Hissene Habre in December 1990.

Deby, who has been slowly hemmed in by the complex ethno-political conflict that started three years ago in Sudan's Darfur region - which borders Chad to the east - does not need reminding.

Recent months have seen a spate of defections of former allies from his ruling Zagawa clan to Darfur-based Chadian rebels. With the Zagawa itself only 1.5 per cent of the country's 10 million-plus population, this was especially ominous for a president with little genuine domestic support.

Moreover, he has lost trust in the wider region due to the split with his original sponsors in Khartoum, and also in Paris.

With Libya, France has long been the major outside influence in N'Djamena, but has never recovered from what it saw as the double game Deby played over the allocation of drilling rights for the Doba Basin oil project in the far south-east during the 1990s.

French oil giant Elf walked out of the project in 1999 for various reasons, and Exxon's subsequent arrival as lead player was felt in Paris as a stinging defeat in the geopolitical game with the United States for influence in African oil territories.

Greater Zagawaland

Despite the continuing presence in Chad of France's 1,000-strong Operation Epervier force, relations remain poor.

For a man whose arrival in power was helped greatly by the French secret services, this was a wrong move.

Meanwhile, regional neighbours have never been comfortable. Gabon has long been an unofficial bolthole for some of Deby's veteran opponents from the Habre era.

Linking all these factors is what now seems to be the simple recognition by virtually all major players in Chad that the Deby era is coming to an end

And Cameroon fears N'Djamena's potential to destabilise its three northern provinces, and has long complained that the heavily-armed zaraguina - highway robber - bands that terrorise key roads in Extrême-Nord Province have been effectively exported from among unpaid elements of the Chadian armed forces.

Others remain unhappy about Chad's involvement in the chaos that has periodically engulfed the Central African Republic since the mid-1990s, much of it the work of Zagawa irregulars - including Deby clan members, who aided current head of state François Bozize to power in 2002.

A telling sign of the balance of opinion turning against the regime is the reported sighting of at least one important ally of Chadian rebel leader Mahamat Nour in Ouagadouou recently.

Under President Blaise Campaore, Burkina Faso has traditionally been close to Deby and was one of his regional sponsors on his march to power.

Then there is the Zagawa question itself.

Even before the age of the internet, rumours have circulated about the Chadian head of state's ambitions for a pan-regional zone of influence, often pejoratively known as Greater Zagawaland.

Assuming that at least some of Sudan's leadership suspect this of their former protégé, it is little surprise that they regard Darfur insurgent groups as a direct threat.

Oil issue

Chad's eastern border now presents not only a military threat, but a financial one too.

Here, Deby's recent dispute with the World Bank is critical. As the key international brokers for Doba, bank staff were horrified in 2005 by Chad's decision to shift millions of dollars from a fund set up to tackle long-term poverty to deal with more pressing financial difficulties.

Chad's rebels are keen to seize power

The bank decided to hold back funds. N'Djamena is now near insolvent, making access to the global arms market difficult. But it is this kind of spending that the bank is determined to forestall.

Finally, rumours deepen about the 56- year-old leader's health. This is important, given his apparent wish to appoint his widely disliked son Brahim as successor.

Many other major Zagawa figures are against that, fearing marginalisation for their own relatives.

Presidential elections are due in May and many people doubt they will be free and fair. If Nour or anyone else feels prepared to take Deby on before the next rainy season, this is their practical deadline to move.

Linking all these factors is what now seems to be the simple recognition by virtually all major players in Chad that the Deby era is coming to an end as the country's post-colonial political vacuum once again opens up.

This time round, even more than when Deby supplanted Habre, the oil issue underlies the thinking of virtually all of them.

Beyond Doba itself, there are promising oil fields elsewhere in southern Chad. Just as important is the potential of major exploration backing from China, which would reduce any future leader's need to depend on the World Bank's say-so.