On 25 April, Australia and New Zealand will observe Anzac Day – an annual Remembrance of all their citizens who have served in conflicts and peacekeeping operations around the world. The day’s origins lie in the Gallipoli campaign from the First World War, which continues to define the two nations’ approach to wars today.

The Gallipoli campaign – which began in February 1915 and lasted until January 1916 – was an attempt by the Entente Powers to weaken the Ottoman Empire and take control of the crucial Suez Canal transport route. It was also the first military operation of the First World War to involve the Australian and New Zealand Armed Forces.

Members of ANZAC (Australian and New Zealand Army Corps) joined the campaign on 25 April, several months after it began. Their objectives were simple: capture Constantinople, the capital of the Ottoman Empire, and knock out one of Germany’s major allies. However, what had been envisioned as a short, sharp shock to the enemy became a brutal, drawn-out stalemate that resulted in tens of thousands of deaths and an eventual retreat by the Entente’s forces several months later.

The land invasion was met by unexpectedly strong resistance, led by a figure called Mustafa Kemal. Later known as Atatürk, Kemal would become the first president of modern Turkey in 1923, when the Ottoman Empire eventually did fall. His victories on the battlefields of Gallipoli earned him a lifelong reputation as one of his generation’s most influential leaders.

Despite the high death toll of Allied forces – including 8,709 Australians and 2,721 New Zealanders – the Gallipoli campaign galvanised the ANZAC alliance, creating a long-lasting legacy of heroism in the face of unbeatable odds. In what could be compared to the Dunkirk spirit that would follow, this Anzac legend quickly spread through Australia and New Zealand and was absorbed into the two nations’ cultural identities.

The fact that so many soldiers had made huge sacrifices, and that they had dug deep to ward off defeat for so long, was inspirational. Anzac Day has been honoured since 1916, and in the 107 years since, it has evolved to encapsulate the spirit of all those who have served in subsequent wars and conflicts.