In today's world, building global peace and security means increasingly preserving and up-holding the institution of the nation-state.

The book's core argument is that today's main threats to global peace and security come no longer primarily from conflicts among nation-states, but increasingly from conflicts within individual nation-states in which weak and dysfunctional governments battle increasingly powerful belligerent nonstate actors. As a result, intrastate armed conflicts have replaced interstate wars as the main “scourge of mankind.” Failing nation-states, especially those with intrastate armed conflicts, not only produce today's great humanitarian tragedies but, more importantly, they are now the main source for global instability. They risk endangering a global system security order that continues to be built on individual but interconnected nation-states that cooperate within a system of international laws, conventions, treaties, and organizations. Such a global security order would need functioning and responsible nation-states. Without this, none of today's global problems can be solved. The breakdown of this order could bring global chaos and, with it, greater human suffering; it could ultimately even lead to renewed interstate wars.

Peacebuilding, the book asserts, is the international response to the threats posed by failing, conflict-ridden nation-states. The book defines peacebuilding therefore as the collective international effort to rescue failing, conflict-ridden nation-states from collapse and to rebuild them into responsible, sovereign members in the global community of nation-states.

For diplomacy, peacebuilding opens an entirely new frontier: the nationstate. While traditionally diplomacy was the art of dealing with international relations, a new diplomacy would instead have to focus its attention on intrastate relations. This would be a major departure from traditional diplomacy. When focusing on intrastate conflicts, a new diplomacy would have to abandon many of its often century-old principles and face previously unknown challenges, many of them wrought with ambiguities and even contradictions:

• i The challenge of defining national sovereignty: Traditional diplomacy is based on the Westphalian principles of national sovereignty and the noninterference in the internal affairs of other nation-states. The UN Charter also explicitly rules out any interference in the internal affairs of member states. However, peacebuilding is exactly this: a deliberate, target-oriented, and time-bound interference in the internal affairs of another nation-state that is unable – or deemed unable – to solve its internal violent conflicts without outside assistance.