The dam broke with the collapse of the Soviet Union in 1991. Suddenly a triumphant West was constructing a "New World Order" in which oppression would be a thing of the past. The Soviet seat in the Security Council was occupied by a diminished Russia, dependent on the West for aid. There was plenty to do. In short order the Council authorised interventions for humanitarian purposes in Iraq (1991), Somalia (1992), Bosnia (1992), Haiti (1994) and East Timor (1999) — more interventions in a decade than had been seen in the previous history of the UN. 

Russian and Chinese discomfort with this wave of Western activism grew, but did not initially stem the tide. Confronted with a likely Russian veto in the Security Council on action in Kosovo (1999), the West simply invented a new legal doctrine ("humanitarian need") to bypass the Council and act anyway. For the 2003 action in Iraq (not primarily humanitarian, but with a large humanitarian dimension), the US and its allies again found legal arguments to bypass the Council. And it was only by mistake that Russia allowed Council assent to military action in Libya (2011). By now, the wind was so much in the sails of the Blair doctrine that there was a serious move to make governments answerable to the international community for the way they treated their citizens — the ultimate abandonment of the non-interference principle. This "Responsibility to Protect" was endorsed by a world summit in 2005. Bismarck must have been spinning in his grave. 

A number of broader points emerge from this history. First, very few interventions have been purely humanitarian. Certainly the Russians went into Bulgaria in 1877 to protect their fellow Slavs, but also to stake their claim to the decomposing Ottoman Empire. India's invasion to stop the 1971 Bengal massacres was additionally prompted by a huge refugee crisis, and the prospect of dismembering Pakistan. Saddam's Iraq was a menace to much more than its own people. And both Bosnia and Kosovo confronted Europe with the prospect of a crime-infested killing ground at its heart. Governments, particularly the US government, have been increasingly reluctant to intervene where they cannot show their publics a direct national interest in doing so. The point is reinforced by one intervention that didn't happen — in Rwanda in 1994 — where perhaps a million people died but the outside world did not feel its interests sufficiently engaged to stop the slaughter. 

Second, the recent history of humanitarian intervention has been one of very mixed success. Some interventions have undoubtedly made the world a better place: Bosnia, Kosovo, East Timor and the British action in Sierra Leone (1999) are examples. On the other hand, the actions in Somalia and Iraq both ended humiliatingly and with many of their aims unachieved. Libya, following the Western action, has collapsed into anarchy. And the prospects do not look good for Afghanistan (again not primarily a humanitarian intervention — but one to which high humanitarian ambitions became attached).