It was in the Somme that the majority of New Zealanders were killed or wounded during the World War 1.

The Battle of the Somme was New Zealand's first major engagement on the Western Front. It took a huge toll on the 15,000 members of the New Zealand Division who were involved. Roughly one in seven of the division who fought on the Somme was killed, and about four in every ten were wounded. More than 2000 New-Zealanders lie buried on what was once the battlefield of the Somme.

Their known graves are cared for by the Commonwealth War Graves Commission (CWGC)

Over half of the members of the New Zealand Division who died on the Somme have no known grave. The names of over 1200 men are inscribed on the New Zealand Memorial to the Missing in the Caterpillar Valley Cemetery west of the village of Longueval.

Cemeteries throughout the area contain the graves of New Zealand soldiers : Dartmoor Cemetery, Warlencourt British Cemetery, Bulls Road Cemetery – the list goes on. It is almost certain that New Zealand's Tomb of the Unknown Warrior at the National War Memorial contains the remains of one New Zealand soldier killed on the Somme in 1916.The remains were interred in the tomb in November 2004. Amongst the 74 bells of The Carillon at New Zealand's National War Memorial are several relating to the Somme offensive of 1916.

Their names echo the places where the New Zealand Division fought and fell in 1916: Delville Wood, Flers, Longueval and High Wood. The bell 'The Somme' is there too, dedicated 'To the Glorious Memory of The New Zealand Division, 1916–18'.

The war took more than 100,000 New Zealanders overseas, many for the first time. Some anticipated a great adventure but found the reality very different. Being so far from home made these New Zealanders very aware of who they were and where they were from. In battle they were able to compare themselves with men from other nations. Out of this came a sense of a separate identity, and many New Zealand soldiers began to refer to themselves as 'Kiwis'.

The total population of New Zealand in 1914 was just over one million. In all, 120,000 New Zealanders enlisted, of whom 103,000 served overseas.
A total of 2688 Maori and 346 Pacific Islanders served in the New Zealand forces.
At least 3370 other men served in the Australian or imperial forces, among them four Victoria Cross winners. In all, 550 nurses served with the New Zealand Expeditionary Force, and many others enlisted in the United Kingdom.
A total of 18,500 New Zealanders died in or because of the war, and nearly 50,000 more were wounded.
Of the total number who died, over 2700 died at Gallipoli, and 12,500 died on the Western Front.

From: http://www.nzhistory.net.nz/war/battle-of-the-somme/new-zealands-somme-experience