When the history of Syria's bloody civil war comes to be written, US President Donald Trump's suggestion that <a href="https://www.thenational.ae/world/mena/donald-trump-us-will-lift-all-sanctions-on-turkey-1.927691">his withdrawal of American forces was a strategic masterstroke</a> will be viewed as an idle boast. The primary purpose of America’s involvement in the conflict was to tackle terrorists who were using the country as a base to launch attacks against the West. And, on that specific issue, the US and its allies can rightly claim to have achieved their goal. ISIS has been destroyed and the terrorist threat has been severely reduced – for the moment, at least. However, as has been demonstrated by America's long and costly involvement in the Middle East dating back to the September 11 attacks in 2001, terror organisations such as ISIS and its Al Qaeda forebears have shown themselves to be remarkably resilient, and have the ability to reconstitute their terrorist capabilities even after suffering the most catastrophic defeats. Thus <a href="https://www.thenational.ae/world/asia/taliban-say-new-afghan-peace-talks-to-be-held-in-china-1.927280">the Taliban in Afghanistan came back stronger than ever</a> after its overthrow by US-led forces in 2001, and similarly Al Qaeda has been able to rebuild its terrorist networks in different parts of the Middle East after suffering a similar fate. And there is every possibility that ISIS will follow a similar path and seek to rebuild its terrorist operations despite the enormous losses it has suffered at the hands of the US-led coalition. It was for this reason that the American military was keen to maintain a token presence in the area, keeping a watchful eye on all the other actors in Syria’s long-running civil war to make sure no new threats emerge that could threaten the US and its allies in the rest. Now, thanks to Mr Trump’s unilateral decision earlier this month to withdraw US forces from their positions along Syria’s northern border, Washington has in effect washed its hands of its involvement in the Syrian conflict, with all the potential security consequences that could have for the US. Congratulating himself on his decision this week, Mr Trump remarked: "Let someone else fight over this long bloodstained sand." Well, the truth of the matter is that the bloodstains might be transferred elsewhere – including American streets – if ISIS and other terror groups are able to take advantage of the vacuum caused by America’s withdrawal. The most obvious winners of Mr Trump’s actions are Turkey and Russia, two countries that have a vested interest in making sure their influence in the country outlasts the conflict Relations between Ankara and Moscow over their involvement in the Syrian conflict have not always been harmonious, especially after the Turks shot down a Russian warplane that had strayed into Turkish air space in 2015. More recently, though, Turkish President Recep Tayyip Erdogan has succeeded in establishing an accord with Vladimir Putin, his Russian opposite number, to the extent that Turkey has agreed a multibillion-dollar arms deal with the Kremlin, including <a href="https://www.thenational.ae/world/europe/turkey-receives-first-parts-of-controversial-russian-s-400-missile-defence-system-1.885434">the purchase of the Russian-made S-400 anti-aircraft missile system</a>. The improved dynamic between Mr Erdogan and Mr Putin cannot, however, conceal the fact that the two leaders are pursuing very different agendas in Syria. Mr Erdogan has long cast covetous eyes over Syria, where he is keen to acquire any territorial gains at the expense of the regime of Syrian President Bashar Al Assad, <a href="https://www.thenational.ae/world/mena/erdogan-is-a-thief-says-assad-on-idlib-frontlines-1.927227">a long-standing rival of Ankara</a>. Russia, on the other hand, is keen to maintain its influence in Damascus, where its military intervention in 2015 at the request of the Assad regime proved decisive in turning the tide of the war in the regime’s favour. The conflicting interests of Turkey and Russia were the key subject of discussion at this week's summit between Mr Putin and Mr Erdogan at the Black Sea resort of Sochi, where the two leaders spent six hours seeking to find <a href="https://www.thenational.ae/world/mena/turkey-and-russia-agree-to-joint-syria-patrols-as-kurds-withdraw-1.927029">a solution</a>. The summit ended with an undertaking that Mr Erdogan can fulfil his ambition of creating a Turkish-controlled "safe zone" in northern Syria, one he claims is necessary to protect Turkey from Kurdish terror cells operating in the area. In return, <a href="https://www.thenational.ae/world/mena/russian-troops-enter-turkey-syria-border-area-1.927600">Russia can have a say in the future of the rest of the territory in northern Syria</a> that has been vacated as a result of the American withdrawal. The deal confirms the increasing influence of Turkey and Russia in Syria at America’s expense. It also provides a much-needed respite for the Kurds who have agreed to withdraw their forces. Turkey in return has announced it will end its military operations in the area. But while the deal will please the Turks and the Russians, it still leaves unanswered the problematic question of what becomes of ISIS following America's withdrawal. There are already reports that ISIS has taken control of some of the vast detention centres in Syria, <a href="https://www.thenational.ae/world/mena/up-to-100-isis-members-escape-al-hol-camp-1.925064">such as Al Hol camp in the east</a>, because the Kurdish forces that were responsible for running them have been moved to deal with the Turkish offensive. Moreover, questions remain about how vigilant the Turks and the Russian-backed Assad regime will be when it comes to thwarting an ISIS revival. Throughout the course of the Syrian conflict, Turkey has had a questionable relationship with Islamist groups in Syria, especially those that are committed to overthrowing the Assad regime. Nor has Damascus shown much interest in tackling ISIS, preferring to concentrate its forces on targeting those groups committed to overthrowing the Syrian government. It is entirely feasible, therefore, that one major consequence of Mr Trump’s actions could be the return of ISIS, a development which not even Mr Trump could claim is a victory for the American people. <em>Con Coughlin is the Telegraph’s Defence and Foreign Affairs Editor</em>