R2P is the international community's organising principle for responding to mass atrocity crimes. It reflected and contributed to the shift from power towards norms as the pivot on which history turns. The old, discredited and discarded 'humanitarian intervention' represents the national interest and power end of the intervention spectrum. R2P is an effort to insert the global justice and normative end and has much better prospects of a convergence of legality and legitimacy in the use of force. It will be easier to prevent unilateral use of force by great powers if their interventionist instincts are moderated by the discipline of multilateral norms. R2P has a secure future because it is demand-driven. On the realism side of the ledger, many leaders rule on the basis of brute force and occasionally will commit atrocities. On the normative side, the better angels of most people in many countries will demand effective and timely action by governments and the UN to halt the atrocities and punish the perpetrators. R2P is the answer to the challenge of global justice being done and being seen to be done, both by states as the primary units of the global order but also by peoples in whom sovereignty ultimately resides. And it does so by reconciling several inherent tensions between competing interests, competing values, and competing interests and values: between the UN Security Council and the General Assembly; between human and national security; between states and the international community; between institutionalised indifference and unilateral intervention; and between the global North and South.