The past, when laid out as a string of events and dates, can make for very dry reading - the sort of rote-learned history that tends to put people off the subject.

However, August 14 is without doubt the most important forgotten date in New Zealand history, and one which deserves to be installed in its proper place in our national memory.

If Waitangi Day was the birth day of the nation, then August 14 was the moment of conception.

On that day in 1839, William Hobson, a Royal Navy captain distinguished only by a very average career to date, was called to the Colonial Office in Downing Street, London, to receive instructions for a new mission: to sign a treaty with the chiefs of New Zealand for a cession of sovereignty - a course for which none of his previous training prepared him to navigate with much competence.

It was one of those history-making moments. After decades of reticence, the British Government finally gave in to the inevitable, and conceded that some type of formal involvement in New Zealand was unavoidable.

The alternative would have been to act as a spectator to growing violence and anarchy in parts of the settlement.

The instructions given to Hobson were issued in the name of Lord Normanby, the Colonial Secretary, but they were almost certainly the work of Sir James Stephen, the sagacious permanent head of the Colonial Office, nephew of William Wilberforce, and a man so powerful that he was known to some of his colleagues as "King Stephen".

The papers handed to Hobson on the evening of August 14 were to have a profound bearing on the future of New Zealand. Arguably everything that has happened in the country in the subsequent 170 years can be traced back to these instructions.

Stephen's brilliance can be seen in every paragraph. The document has an architecture that combines Benthamite idealism, British colonial paternalism and administrative pragmatism, and it was worded in such a way that its meaning could be as pliable as circumstances might demand (this was where his legal training shone through).

And what was the main purpose of this proposed treaty? Well, forget the legal and constitutional arguments, or the more absurd suggestion sometimes raised that it was part of a plan to conquer the country.

"Civilisation" was the word on the lips of colonial officials. Hobson's administration would be armed not with a military force, but with the Office of Protector of Aborigines - a Government department charged with bringing Maori "within the pale of civilised life and to be trained to the adoption of its habits".

Britain was offering an outstretched hand to an uncivilised people, firm in its faith that it could improve the plight of Maori, and save them from what one official described as their "ignorance".

No one in the Colonial Office doubted that the British Empire was one of the great blessings of the age, and that the people of New Zealand should consider it a privilege that they were next in line to be consecrated as a British colony. The use of a treaty was simply the means by which this gift would be bestowed.

Most historians now feel deeply uncomfortable with this rhetoric of civilisation and choose to turn their noses up at the suggestion that any good came of the policy. Yet, in the late 1830s, it was still a radical path to bettering the world, and Stephen was certainly sincere in pursuing it.

He felt the urge to civilise in his bones: it was literally a sacred obligation, not an expedient political response.

However, while the offer of civilisation was there for Maori, there was no plan for Britain to use the treaty to govern New Zealand's indigenous population. On the contrary, British law was to be applied - through the treaty - only to "Anglo-Saxons" living in the country. The extension of British justice to Maori was a process that crept in, awkwardly and unevenly, during the succeeding decades.

Without the instructions issued on August 14, 1839, neither the Treaty of Waitangi, nor the innumerable developments that cascaded from it, would have occurred. This was when the idea of a sovereign New Zealand materialised, and for better or worse, 170 years later, we are the inheritors of that portentous policy.

* Dr Paul Moon is professor of history at AUT.