Many are wondering what it will take to convince Turkey that the threat posed by ISIL is real and that action by Ankara is required as Syria enters its fourth year of civil war.

As things stand, Turkey's policy towards Syria has been to balance its desire to see regime change in Damascus against the regional threat posed by ISIL. However, this policy is unsustainable in the long term.

One event that could forcibly trigger Turkey's entry into the war would be an attack on the Tomb of Suleyman Shah - the grandfather of Osman I, the founder of the Ottoman Empire.

Today, the tomb is a Turkish exclave located inside Syria's Aleppo governorate only 25km from the Syrian-Turkish border. Even though the tomb is located inside Syria, it is sovereign Turkish territory. To complicate matters further, the road from Turkey to the tomb passes through the besieged town of Kobane.

Imperial legacy

Turkey finds itself possessing a tiny piece of territory inside Syria after Suleyman Shah drowned in the Euphrates River in 1236 and his tomb remained under the control of the Ottoman Empire. When the British and the French carved up the Middle East after World War I, the Government of the Grand National Assembly, the precursor to the Republic of Turkey, was keen to keep Suleyman Shah's tomb under Turkish control.

Turkey was granted the tomb and the land surrounding it in the 1921 Treaty of Ankara, which ended the brief Franco-Turkish war. In return, Turkey agreed to recognise French sovereignty over the newly established French Mandate of Syria and Lebanon.

Turkey is viewed by many in NATO as more of a hindrance than a partner under Erdogan's leadership. Many in NATO are puzzled as to why Turkey has not played a bigger role in taking on ISIL.

Article 9 of the Treaty of Ankara states:

"The Tomb of Suleyman Shah, the grandfather of the Sultan Osman, founder of the Ottoman dynasty [the tomb known under the name of Turk Mezari], situated at Jaber-Kalesi, shall remain, with its appurtenances, the property of Turkey, who may appoint guardians for it and may hoist the Turkish flag there."

Almost a century later, Turkey still claims sovereignty over this tiny piece of land - no bigger than two football pitches.

Today, the tomb is defended by Turkish infantry and Special Forces. Even after years of deadly fighting inside Syria, which at times occurs close to the tomb, Turkey has remained committed to its defence.

Attack on NATO?

Last year ISIL threatened to attack the tomb if Turkey did not remove its forces but never carried it out in the end. However, this threat posed an interesting question for western policy makers: Would NATO be obligated to intervene on behalf of Ankara, if attacked, since Turkey is a member of the alliance?

Turkish President Recep Tayyip Erdogan seems to think so. Erdogan has claimed that an attack on the tomb would be an attack on Turkey, and by extension of its membership, an attack on NATO.

In reality, NATO's commitment is not as black and white as Erdogan might think.

The security alliance is based on the idea of collective defence. For NATO and its members, an attack on one is considered to be an attack on all. This commitment to collective defence is made explicitly clear in Article 5 of the 1949 North Atlantic Treaty - the alliance's founding document. Article 6 of the treaty specifically states that NATO's defence guarantee applies to "the territory of Turkey".

But Erdogan should not get his hopes up.

Invoking Article 5 of the North Atlantic Treaty is not automatic. Any country which feels it has been the victim of an attack and wants NATO's assistance must first secure a unanimous vote from all 28 members of the alliance.

Ultimately, invoking Article 5 of the North Atlantic Treaty is a political decision taken by the elected leaders of each member state.

Turkey is viewed by many in NATO as more of a hindrance than a partner under Erdogan's leadership. Many in NATO are puzzled as to why Turkey has not played a bigger role in taking on ISIL.

They have also been put off by Erdogan's crackdown on political dissent, limitations on press freedom, and his drive to bring a more conservative brand of Islam into what is still a largely secular society.

Consequently, in the current political climate it would be inconceivable to believe that all 28 NATO members would vote to invoke Article 5 to defend what many outside Turkey might consider to be a post-imperial anomaly.

One thing is clear: If Turkey is serious about protecting its small patch of territory inside Syria, then it had better be drawing up contingency plans to act alone.

Luke Coffey is a research fellow specialising in transatlantic and Eurasian security at a Washington DC based think-tank. He previously served as a special adviser to the British defence secretary and was a commissioned officer in the United States army.