Jonathan Eyal, Europe Correspondent In London

The challenge posed by Turkey in ISIS battle

Turkey's decision to join the fray and support the war against the Islamic State in Iraq and Syria will reshape the region's power dynamics

The ultimate shape of the Middle East, regional experts have long argued, will not be determined so much by what outsiders either want or plan, but by what the Middle East's own regional powers choose to do.

So it may prove to be the case with Turkey's decision to join the war against the Islamic State in Iraq and Syria (ISIS), also known as the Islamic State in Iraq and the Levant.

The impact of Turkey's involvement in what is increasingly a broader regional war will endure long after the Western military's current bombing campaign is over. And it could transform the Middle East in ways barely imaginable today.

"Turkey is not a country in pursuit of temporary solutions," Mr Recep Tayyip Erdogan, the country's president, told his lawmakers last week, soon after they approved Turkey's entry into the war against the ISIS terrorist organisation.

But the reality is that, like many other countries confronted by the crisis in the Middle East, the Turks improvised at every step, and usually with disastrous consequences.

Initially, Turkey spent years criticising Western governments for refusing to engage with Syria's President Bashar al-Assad despite all the evidence that Mr Assad was an obstacle to any effort to stabilise the Middle East.

But when a revolution against President Assad erupted inside the country, Turkey suddenly changed its tune and started castigating the West for not doing enough to topple the Assad regime.

And as the Syrian government proved more resilient than initially expected, the Turkish government took a calculated gamble by supporting extremist groups inside Syria, as long as these groups promised to hasten President Assad's downfall.

Turkey developed ties to Islamist branches of the so-called Free Syrian Army, as well as to the Tawheed Brigades linked to the Syrian Muslim Brotherhood, and even to Jabhat al-Nusra, the offshoot of Al-Qaeda in Syria.

For a time, Turkish diplomats even pleaded with their American counterparts that Jabhat al-Nusra should not be listed as a terrorist organisation.

The results were catastrophic, for both Turkey and the region. Some of the military equipment now in the hands of ISIS came through supplies which crisscrossed Turkish territory; most of the foreign volunteers now fighting with ISIS came through Turkey, with Turkish border guards pretending not to notice.

To be fair, Turkey was not the only country to get its regional policy wrong: Saudi Arabia and Qatar also tolerated the financing of the same extremist organisations, only to see the consequences literally explode in their faces.

And the US also took its eye off the Syrian civil war, a neglect which contributed to the current Middle East debacle.

Yet no Western politician is now interested in scoring diplomatic points against Turkey by reminding the country of its past mistakes; all have welcomed the Turkish decision to join the fight against ISIS.

And for very good strategic reasons.

As the only Muslim member of Nato, the US-led military alliance in Europe, Turkey's participation adds legitimacy to the anti-ISIS coalition. And it also adds real military heft.

Next to Israel's, the Turkish military is undoubtedly the most powerful in the region.

Turkey's military bases, and particularly the vast airfield at Incirlik in the southern part of the country, will provide a critical boost to the air campaign.

The ISIS militants are surrounded; their plans to carve up an "Islamic caliphate" out of the territory of Iraq and Syria are now certain to be defeated.

Heavy cost of involvement

However, Turkey's involvement may also carry a heavy political cost, both for the US and for the Arab countries of the Middle East.

As Turkish President Erdogan has repeatedly made clear, his real objective in entering the fighting is not so much the defeat of ISIS, but the extension of the war to Syria and the destruction of President Assad's government.

That is the reason that Turkey has renewed calls for the establishment of a no-fly zone in Syria.

It has also called for the creation of safe zones for refugees fleeing the conflict in that country.

The snag is that none of these measures can be accomplished without a substantial US military involvement. So, paradoxically, Turkey's entry into the war against ISIS only complicates America's handling of the crisis by increasing the demands on US power.

And although policy planners in Washington have already rejected demands to expand the war to Syria, pressure from Turkey to do so will increase. "A decisive struggle against all terrorist organisations in the region should be achieved, and Turkey's proposals and warnings should be taken into consideration," said Mr Erdogan, in a direct hint of the political tussles now in the offing.

More importantly, the Turkish involvement will have a direct impact on the fate of the Kurds, one of the few ethnic groups in the Middle East still not to have their own country.

For decades, all Turkish governments have opposed the creation of an independent Kurdish state, fearing that this would encourage the ethnic Kurds inside Turkey - who account for at least a fifth of the Turkish population - to demand their own independence as well.

The slow disintegration of Iraq and the rise of Kurdistan as an autonomous region in northern Iraq is now an accomplished fact which Turkey cannot ignore.

Nevertheless, the Turks want to remain in control of the region, if only to make sure that if Kurdistan does become fully independent, it will not drag with it the Kurds of Syria or the Kurds of Turkey. In short, the Turks are intervening in the hope of becoming the regional arbiters, the midwives of the Kurdish nation. It's not a development which the Kurds themselves welcome.

And although they are too polite to say so in public, no Arab nation is overjoyed by the fact that Turkey has now actively joined the anti-ISIS coalition. The Turkish government has made no secret of its belief that Turkey should resume its role as the dominant power in the Middle East, the true heir to the Ottoman Empire which ruled the region until World War I and which, incidentally, also proclaimed a caliphate over the Middle East. The Turks see their imperial past as glorious; the Arabs view it as one reason for their current misery.

None of these tensions will come to light or become prominent for months, and perhaps not until the ISIS terrorist organisation is defeated. But they are likely to dominate the Middle East in the years to come.

For, a century after they were driven out of the Middle East, the Turkish military is returning to the region. And it is likely to encounter resistance, from the Shi'ite Arabs, who view the Turks as their potential enemies; the Sunni Arabs, who dismiss Turkey as their old oppressor; and the Kurds, who will never accept Turkey as their benevolent patron.

One thing is certain: Slowly but surely, the US and its Western allies are losing their ability to decide the future disposition of the Middle East.