stylistic:style_transfer
The subject of humanitarian intervention has remained a compelling foreign policy issue, especially since NATO's intervention in Kosovo in 1999, as it highlights the tension between the principle of state sovereignty – a defining pillar of the UN system and international law – and evolving international norms related to human rights and the use of force. Moreover, it has sparked normative and empirical debates over its legality, the ethics of using military force to respond to human rights violations, when it should occur, who should intervene, and whether it is effective. To its proponents, it marks imperative action in the face of human rights abuses, over the rights of state sovereignty, while to its detractors it is often viewed as a pretext for military intervention often devoid of legal sanction (as indeed a new customary law norm would require sufficient state practice) selectively deployed and achieving only ambiguous ends. Its frequent use following the end of the Cold War suggested to many that a new norm of military humanitarian intervention was emerging in international politics, although some now argue that the 9/11 terrorist attacks and the US " war on terror " have brought the era of humanitarian intervention to an end.