At its greatest extant under the rule of Suleyman the Magnificent in the 1500s, the Ottoman Empire ran from the walls of Vienna (to which it laid siege in 1529 all the way across eastern Europe and the Middle East to Baghdad and Basra. From Algiers the tughra of the sultans also held sway across the Mediterranean belt of North Africa and encompassed Egypt and territory and peoples on the Arabian peninsula down to Yemen. Its possessions spanned five seas – the Mediterranean, the Aegean, the Black, the Red, the Sea of Marmara and reached the Persian Gulf and the Indian Ocean.

It wasn’t so much an empire a geography syllabus.

And for six centuries on from its conquest of Constantinople by Mehmet II in 1453 (great-grandfather of the Suleyman who the Habsburgs on the ropes in the 1520s) the city on the Bosphorus was the capital of this enormous empire, one which – aside from the Italian landmass and a smattering of Spain – was remarkably similar in span to that last achieved by the Eastern Roman Empire under the energetic Justinian the Great in the 550s.

Not surprisingly, therefore, Napoleon said that if the world were a single country, then Istanbul would be its capital. Because for a very long time it was.

In his book The Caliph’s Last Heritage, Sir Mark Sykes – the Orientalist, diplomat and politician who would one day give his name to one of history’s most notorious international agreements – described the Ottoman empire as ‘a land of contrasts’ and noted it had been the birthplace of ‘the Gospel and the Koran’ and of four great empires.

‘It has been the battleground of all the philosophies and creeds which form the basis of those now occupying Western minds, as well as the highway of all conquerors from Xerxes to Napoleon,’ Sykes wrote. ‘The fact that the decisive historical events which have occurred within the Asiatic provinces of the Sultan are those which have moulded the whole of the spiritual and material destinies of mankind, should give us food for reflection. There is nothing in our daily private or public life today which is not directly or indirectly influenced by some human movement that took place in this zone.’

And so it was. Until it wasn’t. Because in short order things unravelled fast. The last of what was then known as Turkey-in-Europe went – Bulgaria got independence in 1908, Salonica was lost to Greece in 1912 and then in 1913 even tiny Albania, once so loyal, could no longer be retained, leaving the fabled ‘Sick man of Europe’ very nearly a non sequitur. And then, of course, we reach the First World War and the Turks joined the wrong side.

So within a decade of Sir Mark’s travels across the empire in 1913, it was gone, and with it the ancient ruling dynasty ­– the House of Osman – one that had determined the fates of millions of people and millions of square miles of land since inception in 1299. That was when Osman I, a clan chieftain in north-west Anatolia, began what must rank as one of the greatest family enterprises the world as seen, the house of Osmanoglu. It was one which through successive generations and thanks to ‘a continuity of thought and purpose, and a capacity for diplomacy and generalship, unequalled in the history of Oriental dynasties’ (that’s Sykes again) was able to fill the void left by the collapse of the Seljuk Empire, whose capital was in Iran, and capitalise on the geographical limitations of the Cairo-centred Mamluks and the waning of the once-mighty Byzantines.

For a century the Ottoman Empire had been on the skids, hence Britain and France’s efforts to shore up her hold on the Crimea in the 1850s. Now it was terminal. The Turkish patient had ‘not for resus’ posted at the end of its bed.

Turkey capitulated a week and a half before the Germans in 1918, three or four days before the Austrians. The Sultan was still in the Dolmabahce palace overlooking the Bosphorus and presumably had hopes that the show would go on. Well, why not?

But neither he or the politicians running the country knew what was coming, namely that London and Paris had different plans for them altogether. Under the terms of the 1916 Sykes-Picot agreement – secret, though with agreement of Rome or Moscow – Britain and France would carve up the Ottoman empire at the war’s end with the Greeks getting a portion around modern day Izmir. To say that the scheme informed the resulting Treaty of Sevres, signed between the Allies and Turkey in 1920, is an understatement. And unsurprisingly, the Turks weren’t very happy about it.

Among their number was a Salonica-born army veteran Mustafa Kemal Pasha or Ataturk – ‘father of the Turk’s as he would come to be known – who was 40 in 1921 and was undoubtedly as Norman Stone put it, ‘a leader of genius’. Ataturk had had a good war – burnishing his reputation seeing off the British Empire at the Gallipoli, and had advocated breaking up the old tarnished empire and founding a modern Turkish state at least as far back as 1907. He emerged first as a leader of the Turkish National Movement which would seize power from the Sultan’s government in Constantinople (then occupied by the British) and establish first a new Grand National Assembly in April 1920 in Ankara.

That would lead to the abolition of the sultanate in 1922 and the declaration of the Republic of Turkey in October 1923 – by which point Ataturk had become a resistance leader, too, in addition to holding the powerful office of speaker of the assembly. By 1921, having been appointed commander-in-chief, as the Turkish historian M Sukru Hanioglu has observed, ‘Mustafa Kemal wielded more power than any Ottoman sultan or statesman since 1839.’

During what the Turks call their war of independence Ataturk now led the country against a dizzying list of foes – not least the British Empire and France. The Turks drove the Greeks from Anatolia and forced the French back in Syria, creating the outline of what we known as Turkey today, a country and regime both geographically defined and recognised internationally in the Treaty of Lausanne, signed in July 1923 with far better than those enclosed in Sevres.

It was to be a new country, albeit one with ancient antecedents. Its leader, first as prime minister, then as first president would become to Turkey what Lenin was to Russian or Cromwell was to England. A century after his rise his photograph is still ubiquitous in the country that he formed, hanging in cafes, restaurants, railways stations and airports.

Similarly the mark he left on his country has remained. As well as abolishing the monarchy, Ataturk abolished its Arabo-Persian script in 1928 – telling everyone to learn the new language in 10 days. He instead gave Turks a simplified Latin alphabet with the aim of fostering Turkish national identity with the demands of promoting literacy (which doubled to just under 23 per cent by 1940 from 1927). He didn’t stop there. He Turkified the names of Turkish cities, no least Constantinople which was known from 1930 as Istanbul, while Smyrna became Izmir. He had the Koran translated into Turkish and the call to prayer was broadcast in Turkish not Arabic. He gave Turks surnames – by act of parliament in 1934. He adopted modern numerals. He banned the fez, once, ironically, symbol of modernity but now emblematic of backward, decayed Ottomanism. He banned the turban, too. Woman got the vote in 1935. He opened schools, universities, planted millions of trees, reformed agriculture and drove through a process of industrialisation. As well as neutrality internationally – ‘peace at home, peace in the world’ was his slogan – the centrepiece of his vision for the modern Turkish state was secular government: under Ataturk Islam ceased to be the official religion, Parliament no longer followed or passed Muslim canon law, oaths of office were non-religious. The secularisation of the state also had a bearing on the descendants of that Anatolian chieftain, Osman I.

Because although the sultans were gone – the last, Mehmed VI was deposed on 1 November 1922 and exiled, having been declared a persona non grata – his cousin and heir Abdulmejid II, had nonetheless been appointed caliph, the 116th head of the caliphate, through which the Ottoman sultans had claimed leadership of the Islamic world since 1517. It was not, as it turned out, an easy appointment for Abdulmejid – Ataturk refused his requests for robes and finery – and swifty the new president, himself of no religion, moved to have abolish the caliphate altogether. This went hand in glove with Ataturk’s secularist Kemalist creed the secularism – and as Ataturk’s biographer Andrew Mangold noted, with it, ‘the process of secularisation, which had taken a big step forward with the abolition of the caliphate, was now complete.’ In due course Abdulmejid, along with around 100 members of the family, were exiled, and he himself went off to Nice to paint pictures.

Ataturk would continue to lead the country that he helped create until his death in 1938 at the age if 57 from cirrhosis of the liver. ‘At the time few people could envisage that he would be the sole post-Great War leader whose legacy would prevail in his country in the twenty-first century,’ noted M Sukru Hanioglu. Norman Stone compared him with de Gaulle. ‘Both men took credit for subordinates’ achievements,’ he wrote. ‘Both persecuted deserving underlings quite unnecessarily; both might be accused of imposing solutions by authority, whereas more evolution might have been desirable. But they leave a sense of greatness just the same.’

They surely do. During his 18 years at the top of Turkish politics and public life Ataturk oversaw a cultural and economic transformation, and the birth of a national ideal, which naturally enough remains not altogether uncontroversial, particularly to the country’s non-Turkish minorities. Yet for all that, a century on from the country’s last rejection of its Ottoman rulers, Ataturk’s legacy stands, and Turkey itself is arguably stronger than ever.

Alec Marsh is a journalist and the author of After the Flood, the latest Drabble & Harris thriller. You can listen to an interview with Alec on the Aspects of History Podcast