This book concerns the tension between the illegality of a territorial regime (reflected in the principle ex injuria jus non oritur and upheld by the obligation of non-recognition), and its effectiveness (reflected in the principle ex factis jus oritur). It examines the manner in which this tension informs the policy of post-transition regimes, namely the extent to which post-transition regimes attempt to reverse the factual situation created by preceding illegal regimes, and the extent to which they succeed, in light of the legal and political constraints in which they operate.

Under international law, acts that are in contravention of a peremptory norm are invalid ab initio. When a territorial regime is created in violation of such norms, its illegality and the invalidity of its acts are upheld by the obligation of non-recognition. The goal of this obligation is to ensure that the illegal regime cannot consolidate itself in the territory. This is intended to induce that regime to withdraw, thereby bringing the violation of the peremptory norm to an end.

However, in reality the power of non-recognition is limited, and illegal regimes have managed to exist for lengthy periods of time. At times the weakness of non-recognition lay in its non-uniform application, for example in the cases of the Soviet annexation of the Baltic states and the Indonesian annexation of Timor-Leste. In other cases, the illegal regime was strong enough to withstand isolation. Such was the case of Rhodesia.