<p>This thesis is an in-depth study into the New Zealand-Australian relationship and the two nations' divergence in International Relations, with particular reference to the disparate foreign and security policies implemented under the Howard and Clark Governments from 1996/1999 respectively until the present time in 2007. The purpose of this study is to provide an accurate and up-to-date overview of the New Zealand-Australian relationship as it stands today, and to define the main areas of difference between the two countries which are driving trans-Tasman divergence in the international sphere. In pursuit of this goal, the subject-area is explored in the following ways. Chapter One provides a general overview of the trans-Tasman relationship, reflecting specifically on three abiding dynamics which together have contributed to the 'strangeness' of the trans-Tasman rapport from the mid-1800s until today. Chapter Two, defines in fuller detail the greatest areas of divergence between the two countries in their foreign and security policies, and then additionally outlines three important issues in the international sphere on which the Tasman pair have diverged most strikingly in recent years. Chapters Three to Five explore three areas of fundamental difference between the Tasman pair in their International Relations, considered here to be driving factors behind the trans-Tasman divide - namely, different beliefs and approaches towards multilateralism, the use of force and relations with the United States. Finally, Chapters Six and Seven explore three contemporary theories attempting to explain New Zealand and Australia's divergence in International Relations today. There are three main arguments throughout this thesis: first, that New Zealand and Australia are becoming increasingly divergent in their foreign affairs; second, that this divergence is primarily due to the fact that the two countries are fundamentally different in their views and approaches towards three crucial areas within international politics - multilateralism, the use of force and relations with the United States; and thirdly, that these differences in view and approach, and the divergent policies they produce, in turn arise chiefly from completely disparate senses of national identity in the two Tasman countries, which motivate differing - and sometimes conflicting - foreign policy behaviour. These three arguments are explored and expounded in the following ways. With regard to the first argument, Chapter Two provides an in-depth overview of the most important areas of divergence between New Zealand and Australia since 1999. As to the second argument, Chapters Three to Five employ a case study based on discourse analysis into New Zealand and Australian governmental speeches on the 2002-2003 Iraq Crisis - an issue that inherently involved these three fundamental areas of difference - in order to specify how precisely New Zealand and Australia diverge in their view and approach to these three matters based on the two Governments' own self-proffered statements and explanations. These disparate beliefs are then shown to translate into divergent actions and foreign policy behaviour on the world stage, by substantiating such rhetorical statements with evidence taken from the Howard and Clark Governments' foreign policy record, as documented in governmental documents as well as in political and academic literature. Finally, with regard to third argument, Chapters Six and Seven involve a discussion and critique of two rather convincing orthodox explanations for trans-Tasman divergence, Hugh White's 'Strategic Perception' and David McCraw's 'Divergent Political Ideologies', as well as a summary and broad application of one new theoretical explanation called 'Identity Theory' to New Zealand and Australia's foreign policy record, in order to show that it is indeed identity-based explanations, when combined with other strategic and political factors, that in fact provide the most accurate, comprehensive and insightful explanation for New Zealand and Australia's divergent behaviour in the international sphere from the time of Federation in 1901 until today in 2007. This thesis makes the following conclusions: first, that it is fundamentally different beliefs in regard to multilateralism, the use of force and relations with the United States which are driving the 'continental drift' between New Zealand and Australia, through motivating disparate policies and conflicting behaviour by the Tasman pair in their international affairs, as shown during the 2003 Iraq Crisis; secondly, that these dissimilar beliefs regarding the three matters stem in turn from deeply-rooted foreign policy traditions within New Zealand and Australia's own core national identity, namely traditions of independence, idealism and multilateralism in New Zealand, and independence, realism and alliances in Australia; and thirdly, that it is in fact national identity - encompassing national beliefs, traditions and ideas of what the nation stands for and is destined to become - that can best explain nation-state behaviour and action on the world stage today. In my own view, I believe that it is identity theory, when combined with aspects of disparate strategic perception and predominant governmental political ideology advocated by White and McCraw, which together present the best and most wide-ranging means of understanding the complex realities of International Relations today. It is hoped that the research undertaken in this thesis will not only contribute to the new wave of academic literature attempting to describe and explain the differences between New Zealand and Australia in our foreign affairs today in 2007, but also add to the growing consensus in the constructvist academic world that identity-based explanations are crucial for understanding foreign affairs.</p>