Anzac Day is a national day of remembrance in Australia, New Zealand and Tonga that broadly commemorates all Australians and New Zealanders "who served and died in all wars, conflicts, and peacekeeping operations" and "the contribution and suffering of all those who have served". Observed on 25 April each year, Anzac Day was originally devised to honour the members of the Australian and New Zealand Army Corps (ANZAC) who served in the Gallipoli campaign, their first engagement in the First World War (1914–1918).

Anzac Day marks the anniversary of the first campaign that led to major casualties for Australian and New Zealand forces during the First World War. The acronym ANZAC stands for Australian and New Zealand Army Corps, whose soldiers were known as Anzacs. Anzac Day remains one of the most important national occasions of both Australia and New Zealand. 

In 1915, Australian and New Zealand soldiers formed part of an Allied expedition that set out to capture the Gallipoli Peninsula in the Ottoman Empire to open the way to the Black Sea for the Allied navies. The objective was to capture Constantinople, the capital of the Ottoman Empire, which was a member of the Central Powers during the war. The ANZAC force landed at Gallipoli on 25 April, meeting fierce resistance from the Ottoman Army commanded by Mustafa Kemal (later known as Atatürk). What had been planned as a bold strike to knock the Ottomans out of the war quickly became a stalemate, and the campaign dragged on for eight months. At the end of 1915, the Allied forces were evacuated after both sides had suffered heavy casualties and endured great hardships. The Allied deaths totalled over 56,000, including 8,709 from Australia and 2,721 from New Zealand. News of the landing at Gallipoli made a profound impact on Australians and New Zealanders at home and 25 April quickly became the day on which they remembered the sacrifice of those who had died in the war.

Though the Gallipoli campaign failed to achieve its military objectives of capturing Constantinople and knocking the Ottoman Empire out of the war, the actions of the Australian and New Zealand troops during the campaign bequeathed an intangible but powerful legacy. The creation of what became known as an Anzac legend became an important part of the national identity in both countries. This has shaped the way their citizens have viewed both their past and their understanding of the present. The heroism of the soldiers in the failed Gallipoli campaign made their sacrifices iconic in New Zealand memory, and is often credited with securing the psychological independence of the nation.

Read more on the Wiki ANZAC entry

Visit the Australian War Memorial for more information on ANZAC Day