New Zealand Military Records
The first instance of a New Zealand conflict came early in the 19th century land wars, where colonists subdued the Maori. Since then New Zealand troops have been involved in many conflagrations, beginning with the Boer War. Family historians are lucky as there is open, easy access to all the records. The only problem is that at present these records are in two different locations. You can find many of those from the Boer War and the First World War at Archives New Zealand, whilst newer files are with the New Zealand Defence Force Personnel Archives. However, the records will soon all be merged at the Archives.
Home ForcesNew Zealand needed a militia that could be rapidly mobilised. This became possible under the 1845 Militia Ordinance, with the Volunteer Corps taking over the duties during the 1860s. It was followed by the Colonial Defence Force, which existed until 1867, to be replaced by the Armed Constabulary, a unit that existed until the 1880s. There are rolls and lists for all these groups available in the National Archives.
If your ancestor fought in the 19th century land wars, he might have been eligible for a New Zealand War Medal, although this was only awarded to colonial soldiers who could prove they'd been under fire (the British militia received theirs automatically!). The Archives have medal applications in the Wellington office and each one contains a short description of the soldier's service, which can help flesh out the portrait of an ancestor.