It is only in a most imprecise sense that New Zealand can be said to have had any international relations before 1919. Apart from a possibly absent-minded attempt to open direct trade negotiations with the United States in 1870, and a trivial agitation in 1869–70 for separation from Great Britain, New Zealand's external affairs before 1919 are inter-imperial rather than international.

Her entry into the 1914–18 war was the action of a dependent country. But her participation in peace making was of a different order. The New Zealand delegation to the Paris Peace Conference, led by Massey, was accepted as a rather indeterminate subdivision of the whole British (i.e., British Empire) delegation. Massey argued obstinately and successfully for New Zealand interests. He signed the Peace Treaty in a manner that avoided the question: did New Zealand do so as an independent power or not? He himself had little time for theory and was an intense loyalist. When, back in New Zealand, he was charged with an action which assumed the essential independence of New Zealand, he denied the imputation. He had been concerned with limited, concrete objectives: a mandate conferring very full powers over Western Samoa, captured by New Zealand from Germany in 1914, and a voice in the control of phosphate-rich Nauru Island.

Others were more concerned with theory. W. Downie Stewart, a colleague of Massey, pointedly questioned the premier on this matter of independence. Sir Francis Dillon Bell, the representative at the League during the 1920s, shared Massey's loyalist conservatism but not his vagueness. He drew a lawyerlike distinction between the full status of an international power, and the partial assumption of that status for strictly limited purposes. New Zealand, he concluded, solely for the purposes of League membership consented at times to act as if she was independent.

If it should be concluded that in this period New Zealand sought to combine the advantages of dependence with those of independence and that her statesmen accordingly avoided clear definitions as if they might bite, that conclusion would be true. The clue to the ambiguity is security, and security, as the policymakers from 1919–35 agreed, was best achieved by acting the role of dutiful imperial daughter. When a change came, as it did after 1935, it was not because the security motive had been replaced by a different one, but that alternative or complementary ways of achieving security were then advocated. Nor, after 1935, did mere dutifulness any longer seem a reliable guarantee. The idea that security and British dependence could not be straightforwardly equated prevails from 1935 to the present day. It would be fair to say, in brief, that the unambiguous assumption of full international status was, whatever it might have also been, at least a new answer to the problem of national security.

The Labour Government, between 1935 and 1939, exhibited both the idealism of the left and the practicality of the rulers of a small nation. They supported the League because the League stood for peace (a conclusion towards which Coalition leaders had also significantly advanced by 1935), and peace, in itself a high ideal, was also an avenue to security. In these years the United Kingdom Government followed policies in respect to Japan, Germany, and Italy, which, to the New Zealand Labour Government, seemed risky and even immoral. They turned to the League as the fountainhead of international morality, and to the concept of collective security as the surest guarantee of New Zealand's, and all small nations', integrity. Accordingly, within the League New Zealand and Great Britain sometimes took opposite sides, notably over the question of Italian aggression in Ethiopia. While New Zealand, perhaps unrealistically, advocated firm collective action, Great Britain accepted the course of “great power” negotiation outside the League, leading eventually to a recognition of the Italian conquest.

The events of these years, during which New Zealand can be said to have come of age internationally, do not imply any weakening of the ties between Great Britain and New Zealand. Loyalty was amply demonstrated when war broke out in 1939 and New Zealand unhesitatingly joined Great Britain. But New Zealand fought this war as an ally; her forces were ultimately under the control of her own Government, though commonly that Government yielded to the requests of the senior partners in the Grand Alliance.

The year 1942, when Japan attacked in the Pacific, marks another departure. For a few months in 1942 New Zealand was defenceless; when the rescue came it was American, not British, thus palpably demonstrating an already plain fact. Security was something the United Kingdom, during a world conflict, could no longer guarantee in the Pacific Ocean. Subsequent developments in New Zealand international relations stem, in considerable part, from the implications of this fact.

By the mid-twentieth century the realities of international life had impressed themselves indelibly. Remoteness and vulnerability to any threat in the Pacific has alarmed politicians since the later nineteenth century; the might of the Empire and the navy had been set in the scale against the menaces. In the 1920s there were protests against British Government disarmament proposals; in the 1930s British guarantees against Japanese aggression were sought and secured. In 1942 the embattled British Government tried in vain to fulfil them; New Zealand's integrity was preserved by the United States.

The ANZUS Treaty, signed in 1951, was the consequence. Australia, New Zealand, and the United States here undertake to defend each other against attack. For New Zealand and Australia the power to be feared was Japan, which the United States wished to rehabilitate quickly as a counter to the Communist threat in Asia. The treaty continues as a protection from that threat. This dependence upon America as a Pacific power, rather than upon the British connection, has become the cornerstone of New Zealand's international relations.