New Zealand enters the First World War

Britain declared war on Germany on 4 August 1914, after German forces invaded Belgium. The king acted on the advice of his British ministers alone, and neither New Zealand nor any other part of the empire was consulted, although Te Ara notes that as a self-governing dominion New Zealand could still choose whether to send troops overseas. Wellington received the news at 1 p.m. on 5 August, New Zealand time, and the governor, Lord Liverpool, announced it from the steps of Parliament; NZHistory gives the crowd as more than 12,000 in one account and 15,000 in another. Prime Minister William Massey pledged support for the empire immediately. Te Ara explains New Zealand's willingness in terms of sentiment, economic interest and security: most New Zealanders thought of themselves as British, the country depended on the British market for its farm exports, and it looked to British sea power for its safety. The declaration brought 14,000 volunteers to Defence Department offices.

On 6 August Britain asked New Zealand to seize German Samoa, with its wireless station at Apia, as a 'great and urgent Imperial service'. A force of about 1400 under Robert Logan landed at Apia on 29 August without resistance; Te Ara gives its strength as 1,374. It was the second German territory, after Togoland in Africa, to fall to the Allies. The main body of the New Zealand Expeditionary Force (NZEF), about 8500 soldiers with more than 3000 horses, left Wellington in 10 troopships on 16 October 1914. The Ottoman Empire's entry into the war changed their destination, and they disembarked in Egypt. In April 1915 they landed on the Gallipoli Peninsula, where 2779 New Zealanders died (see The Gallipoli landing). From 1916 the New Zealand Division fought on the Western Front in France and Belgium, where almost 12,500 died, about 843 of them at Passchendaele on 12 October 1917 (see Passchendaele — the worst day). A mounted rifles brigade served in Sinai and Palestine.

As the war dragged on it grew harder to find enough men, and by late 1915 volunteers were falling short. The Military Service Act, passed on 1 August 1916, allowed the government to call up any man aged between 20 and 45 (Te Ara says 46). NZHistory dates the first ballot to 16 November 1916; Te Ara says the first ballots were in October. NZHistory calculates that of the 98,850 New Zealanders who served abroad, 80% were volunteers and 20% (19,548) conscripts; Te Ara gives a higher figure of 32,000 conscripts. NZHistory also records that 286 conscripts who refused any form of military service were court-martialled and imprisoned. At home, women increasingly filled gaps in the labour force, and the rising cost of living brought industrial disputes on the wharves and in the coal mines in the last two years of the war.

Māori were at first generally excluded from the NZEF, because the war was assumed to be a 'white-man's war', but a Māori contingent followed the main body, and more than 2200 Māori served overseas. Many Waikato–Tainui and Taranaki Māori, whose land had been confiscated in the 1860s, would not fight for the British Crown. Te Puea Hērangi held that her grandfather, King Tāwhiao, had forbidden Waikato to take up arms again when he made peace with the Crown in 1881. Conscription was extended to Māori in 1917 (in June, says one NZHistory page; in late 1917, says another) but applied only to the Waikato–Maniapoto land district, and the first Māori ballot was held in May 1918. Te Puea gathered men liable for conscription at Te Paina, the pā (village) she had rebuilt at Mangatāwhiri near Mercer, where police arrested several on 11 June 1918. By 1919 only 74 of the 552 Māori called up had gone to camp, and none was sent overseas. NZHistory judges that the wounds were probably only healed by the Tainui Treaty settlement in 1995.

An armistice on the Western Front took effect at 11 a.m. on 11 November 1918, and at home the celebrations were marred by the influenza pandemic (see The influenza pandemic). Te Ara says 104,000 men and women left New Zealand to take part in the war, from a population of just under a million, and that nearly one in five did not return; NZHistory puts the population at just over a million and those who served overseas at about 100,000. The official roll of honour now counts 18,058 war dead, and NZHistory records 41,000 instances of wounding or illness. Te Ara says New Zealand had the highest percentage (5%) of its military-age men killed of any dominion of the British Empire. In 1919 Massey signed the Treaty of Versailles for New Zealand, which joined the League of Nations as a member in its own right. The first Anzac Day services were held on 25 April 1916, and the names of the dead are recorded on about 500 civic war memorials around the country.