Rising Great Power tensions in the early 20th century and the interwar period led to a breakdown in the concerted will of the international community to enforce considerations of a humanitarian nature. Attempts were made under the auspices of the League of Nations to arbitrate and settle international disputes. Aggressive actions, such as the Italian Invasion of Abyssinia and the Japanese occupation of Manchuria were condemned, but the League lacked the resolve to enforce its will effectively. The Allied discovery of the Holocaust and the subsequent Nuremberg trials at the end of World War II caused attitudes to change considerably. After the tragedies in Rwanda and the Balkans in the 1990s, the international community began to debate how to react to cases in which human rights are grossly and systematically violated. Especially, in his Millenium Report of 2000, then Secretary-General of the United Nations Kofi Annan, called on Member States: "If humanitarian intervention is indeed an unacceptable assault on sovereignty, how should we respond to a Rwanda, to a Srebrenica, to gross and systematic violations of human rights that offend every precept of our common humanity?". Since the end of the Cold War, interventions have increasingly been used, such as the NATO bombing of Yugoslavia and the 2011 military intervention in Libya.