Less than 1500m wide at its narrowest point, the Strait of Çanakkale (Çanakkale Boğazı), better known to English-speakers as the Dardanelles or the Hellespont, has always offered the best opportunity for travellers – and armies – to cross between Europe and Asia Minor.

King Xerxes I of Persia forded the strait with a bridge of boats in 481 BC, as did Alexander the Great a century and a half later. In Byzantine times it was the first line of defence for Constantinople, but by 1402 the strait was under the control of the Ottoman Sultan Beyazıt I (r 1390–1402), which allowed his armies to conquer the Balkans. Beyazıt's great-grandson Mehmet the Conqueror fortified the strait as part of his grand plan to conquer Constantinople (1453), building eight separate fortresses. The strait remained fortified after he defeated the Byzantines, signalling to foreign powers that this strategic sea passage was firmly in Ottoman hands.

The Ottomans remained neutral at the outbreak of WWI, but in October 1914 they joined the Central Powers and closed the Dardanelles, blocking the Allies' major supply route between Britain, France and their ally Russia. In response, the First Lord of the British Admiralty, Winston Churchill, decided that it was vitally important that the Allies take control of both the strait and the Bosphorus, which meant capturing İstanbul. His Allied partners agreed, and in March 1915 a strong Franco-British fleet attempted to force the Dardanelles. It was defeated on 18 March in what the Turks commemorate as the Çanakkale Naval Victory (Çanakkale Deniz Zaferi).

Undaunted, the Allies devised another strategy to capture the strait. On 25 April, British, Australian, New Zealand and Indian troops landed on the Gallipoli Peninsula; in a diversionary manoeuvre, French troops landed at Kum Kale near Çanakkale. The landings on the peninsula were a disaster for the Allies, with the British 29th Division suffering horrendous losses at Cape Hellas and the Anzac troops landing at a relatively inaccessible beach north of their planned landing point near Gaba Tepe (Kabatepe). Rather than overcoming the Turkish defences and swiftly making their way across the peninsula to the strait (the planned objective), the Allies were hemmed in by their enemy, forced to dig trenches for protection and stage bloody assaults to try and improve their position. After nine months of ferocious combat but little headway, the Allied forces withdrew in December 1915 and January 1916.

The outcome at Gallipoli was partly due to bad luck and leadership on the Allied side, and partly due to reinforcements to the Turkish side brought in by General Liman von Sanders. But a crucial element in the defeat was that the Allied troops landed in a sector where they faced Lieutenant Colonel Mustafa Kemal. A relatively minor officer, the future Atatürk had managed to guess the Allied battle plan correctly when his commanders did not, and he stalled the invasion in spite of bitter fighting that wiped out his regiment. Kemal commanded in full view of his troops throughout the campaign, miraculously escaping death several times. Legend has it that at one point a piece of shrapnel hit him in the chest but was stopped by his pocket watch. His brilliant performance made him a folk hero and paved the way for his promotion to paşa (general).

The Gallipoli campaign – in Turkish the Çanakkale Savaşı (Battle of Çanakkale) – resulted in a total of more than half a million casualties, of which 130,000 were deaths. The British Empire saw the loss of some 36,000 lives, including 8700 Australians and 2700 New Zealanders. French casualties numbered 47,000 (making up over half the entire French contingent); 8800 Frenchmen died. Half the 500,000 Ottoman troops were casualties, with almost 86,700 killed.