The caliphate had acted as a basis for unity, identity and authority for hundreds of years. Its demise brought a disruption of political authority that has lasted until the Arab Spring
End of the caliphate left Arab nations searching for identity
In the early hours of March 4, 1924, a middle-aged man and his family left the Dolmabahce Palace in central Istanbul and headed to the train station.
Their destination was Switzerland and then Paris, where the man, Abdulmecid II, died 20 years later, and was buried in Medina.
Abdulmecid II was the last caliph of Islam, the end of a line of religious and political rulers that had stretched back unbroken to the time of the Prophet Mohammed.
The end of the Ottoman Empire had come two years earlier, when it was replaced by the Republic of Turkey. With the exile of Abdulmecid II, the caliphate was officially abolished. The implications of that administrative act have proven to be sweeping, although barely expected at that time.
The Turkish authorities expected public resistance - and got it in the form of demonstrations and protests, which ran for months and were often brutally suppressed. But the longer-term effect could not have been foreseen. The repercussions of the end of the caliphate are still being felt.
The importance of the caliphate to the wider Muslim world was not in terms of religion, but instead of identity. The authority of Istanbul had been weakening for some time, not only in politics but also in its ability to provide religious leadership for hundreds of millions of Muslims across the globe. Other competing ideas about Islam were coming, meanwhile, from Iran and Saudi Arabia.
But the caliphate was more important as a unifying institution, indeed as an idea. Since the coming of Islam in the 7th century, the caliphate in its various forms had provided a framework for the unity and identity of Muslims, an institution for the expression of the faith and, most importantly, a basis for political authority.
It was that last part that turned out to be vital, so that its removal has contributed to the lack of stability of the Middle East ever since.
Political authority is the basis on which communities of people - nations for example - are held together. In political science, in what sounds like a tautological formulation, a government is legitimate in so far as there is a broad recognition from a majority of the people that the government is legitimate. The source of this legitimacy can of course vary: democratic elections, hereditary lineage, and control of institutions are a few examples.
But the broad point is that most people in such a community will feel the leaders have a legitimate claim to lead.
The end of the caliphate disrupted political authority in the Islamic world, especially in those nations that looked towards Istanbul.
With the caliphate gone, the basis of political authority all but vanished. Previously, there had been at least an implied religious underpinning: Arabs lived together in states whose leaders derived their authority from the Ottoman Empire and whose political authority, in turn, was derived from religious authority. It was because the Ottomans claimed to uphold Islamic law that they could also practise terrestrial authority.
With that gone, Arab peoples had to formulate new ways of living together.
The colonial powers tried to enforce the idea of nation states, but drew the boundaries in ways that did not take into consideration how people actually lived, or what they wanted. People of different faiths and sects were shoved together in a new Iraqi state; the whole of the Levant was carved into smaller pieces.
The repercussions of creating such unrealistic borders are still with us: they are part of the reason why Iraq has been fractious for decades and was ruled by force for so long, and why Lebanon and the rest of the Levant continues to flare up in sectarian conflicts.
Since the end of the caliphate, there have been many questions about the bases of political authority in various Arab countries.
One way to view the past century, and in particular the postcolonial period and the Arab Spring, is as a series of attempts to articulate different forms of political legitimacy.
Should countries be held together on the basis of religion, or of language, or of political ideas (for example secularism), or simply because of geography?
The events of the Arab Spring can be seen as another attempt to forge new national identities to replace the supranational religious identity of the caliphate.
There are still intermittent movements to bring back the caliphate in some form or another.
But the modern Arab world has broadly accepted the borders imposed upon it during the colonial period, and has attempted to find a way of organising politics and society to make the current nations work. The Arab Spring is the latest such attempt, and, we can hope, will be the most lasting.
When Abdulmecid II stepped onto a train one morning 89 years ago, he - and the leaders who replaced him - could little have imagined that almost a century later the effect of his exile would continue to convulse the entire region.
On Twitter: @FaisalAlYafai