Blogger's Note: This is a rather long post, and for such a long post it is rather dry. The key point I'm making is in the last paragraph; the intervening 1700 words are all framing and support, so feel free to skip them (or go back to them).
Wikipedia, that stalwart of internet reliability, lists 60+ wars that started since 1991. As an added bonus, they have an ongoing wars page, which includes some conflicts that are carryovers from the previous century. It's interesting, and a way bigger list than I was intending to write about. So I'll just point you in that direction and move on.
The big thing I was looking for was wars authorized by the Security Council since the end of the cold war. Reading "Chasing the Flame", four big wars stand out, to my American/Anglo biased perspective. These are the Persian Gulf War, the Kosovo War, Afghanistan, and Gulf War II. Appropriate big omissions of foreign military intervention are Rwanda and Darfur.
The last 20 years was bigger than this, with more going on, but these 6 conflicts give us an interesting opportunity to examine war's legality, legitimacy, and underlying motive. Each of these conflicts can have a case made for or against Humanitarian War. Each conflict, case-by case:
1. Persian Gulf War
Legal? Yes, authorized by the UN Security Council
Legitimate? Yes. A coalition expels an invading/occupying force from a sovereign nation.
Humanitarian? Debatable. The crimes committed by Saddam Hussein, the huge, morally reprehensible ones, were against populations living with Iraq, were committed in the late 80s, and were largely unrelated to the invasion of Kuwait. Likewise, the victorious coalition hurt the regime and ended the occupation, but they stood by while purges were enacted against populations within Iraq; the Shi'a were most hurt, while the US managed to intervene to help the Kurds later in Northern Iraq. All this distracts from the point; the war had the chance to be humanitarian, chose not to be, and instead operated in defense of sovereignty.
Legal? While earlier NATO bombing had been supported by the UN, the actual move to defend and liberate Kosovo was taken without either the permission or the explicit opposition of the Security Council. This is a grey area, but the war probably falls on the side of illegal.
Legitimate? Many within the UN tended to view it as such, and it was a war against a previously-proven genocidal government.
Humanitarian? Most would agree that it was, but the nature of the war (bombing campaigns) hurts the image of NATO as concerned for the best interests of civilians. That the ethnic Albanians were oppressed, being exterminated, and then saved by the war is more certain.
Legal? Since it was not an officially declared war, it was not illegal, but it had no immediate legality. The UN Security Council later authorized an "international security assistance force", which can be assumed that the post-Taliban occupation is more legal.
Legitimate? Unclear. That the Taliban Regime* oppressed it's people is a well-documented historical fact, and that the Taliban regime engaged in both ethnic and religious conflcit isn't disputed. It was, in the eyes of the international community, an illegitimate regime, reocgnized prior to 9/11 by only 3 nations, and shortly afterwards by only 1. But no war has had legitimacy simply by saying "this government oppresses it's own people, let us overthrow them". The war's stated reason was that the Taliban gave support to Osama bin Laden and al Qadea (which the Taliban, in fact, did), and that Osama bin Laden was the chief planner of the 9/11 attacks (still not proven). The war is almost legitimate, and by almost all still probably considered a good thing.
Humanitarian? As mentioned above, the Taliban was an oppressive regime, and very few mourned it's overthrow. Afghanistan, as a country that has suffered war more or less continuously since 1979, had a brief period of stability when the Taliban assumed control of msot of the nation in 1996. The Northern Alliance and the Taliban still fought, however, which means that the risk of ending a cruel but peaceful era was not a big one. The war is plausibly humanitarian, and what would tilt the balance either way is the nation-building undertaken afterward. The humanitarian objectives that are pursued are several levels below military ones, so I'm going to have to rule this a no.
*Regime has become such an ugly word, but it still seems to be the most appropriate one
Legal? No, war undertaken after a UN veto of the war
Legitimate? Not on the grounds of preventative war, as Saddam's threats were empty, and if it was a war explicitly against a decades-old ethnic cleansing, then it is unprecedented and failed as well.
Humanitarian? Saddam Hussein was a vicious leader, but replacing a tightly-controlled, stable and oppressive state with the world's number one breeding ground for terrorism and a civil war both count against the humanitarian virtues of the war.
Legal? Was a civil war; saw no UN military intervention/authorization
Legitimate? Was a genocidal civil war; the UN abandonment of it's duty there has been decried as a horrific failure, and itself eroded the UN's legitimacy.
Humanitarian? Not going to war saved the UN from a difficult task of intervening in a civil war. Involvement in such a civil war would have meant placing UN peacekeepers in such a fashion so as to stand between two hostile groups and hope they can hold, or to choose a side and risk the death of innocents. Failure to intervene with armed force, it can be argued, is what made Rwanda Rwanda, as the ultimate example of inaction and atrocity in the face of inaction.
Legal? The civil war is seen as having an element of ethnic cleansing, making it illegal even by the standards of a civil war. An African Union peacekeeping force has been present for a while. Recently, a joint UN-AU peacekeeping force
Legitimate? The involvement by the African Union is widely acknowledged as a good thing; the UN itself formed a joint mission with the African Union. Sudan views it as illegitimate, but in places where sovereignty has collapsed the international community has a vested interest, and Darfur certainly qualifies as a collapse of sovereignty.
Humanitarian? The protection of humanitarian operations is an explicit objective of the UN/AU mission, and the usage of both military and police forces entails a strong Humanitarian objective.
** Rwanda and Darfur get big qualifiers because they are not wars engaged in for humanitarian purposes; they are humanitarian crises involving war in which it is hypothesized that armed intervention by an international force may have had humanitarian benefits, and brought about a humanitarian resolution of the crisis. In Darfur, we may be able to witness this happen.
The conflicts of this era are especially important as they more closely resemble the conditions in which the League of Nations was formed and failed. While the UN grew up in the Cold War, it's changed role from mediator between two bitterly opposed worldviews (a mediator that happens to intervene in crises from time to time). Post Cold War, the UN has become the sole source of international legitimacy, and has to deal with a myriad of unbalanced partners in conflict. To better understand these humanitarian wars in conflict, lets look at a pair of wars, from the League of Nations era, where humanitarian concerns were relevant.
7. The Spanish Civil War
Legal? As a civil war, the assumed protocol was to keep out of it, and many nations refused to sell arms to either group of belligerents. This was ignored by the three major nations that interfered in Spain; Fascist Italy, Nazi Germany, and Soviet Russia.
Legitimate? Intervention and arms-selling was viewed as illegal and immoral by most Western Democracies, so if we are using their standard of legitimacy foreign intervention was illegitimate. However, the Soviets, and the Fascists/Nazis, both felt involvement in such a conflict was an ideological imperative, and felt their involvement was justified. Several foreign nationals felt that serving in Spain (esp. on the side of the Republic) was a personal moral imperative, and volunteered; this alone the League of Nations enacted a formal ban against.
Humanitarian? The League's abstention from involvement in this conflict was one of many instances of the League's failure to prevent war, and the ban on foreign nationals was viewed by many as a guarantee of Franco's victory. The volunteers felt a humanitarian and a moral imperative, so armed intervention could have been viewed as humanitarian had it been undertaken solely by altruistic individuals. The history of armed intervention in Spain involves far-reaching concerns, but very few of them altruistic or humanitarian.
8. World War II
Legal? The belligerents in WWII simply left the League, removing any authority it may have had over their actions.
Legitimate? Certain sides can not be counted as legitimate; Lebensraum is not an acceptable political justification for war. The Allies, as glorified in history, fought for the freedom of Europe (and other parts of the world), and so they have that whole moral justification back story. Since they were attacked, and since the Nazis committed massive crimes against humanity, it's easy to gloss over as legitimate. Excepting that the Holocaust was barely known, much less a justification for war. And excepting the history of the USSR, which attacked non-belligerent nations, and whose people often tried to openly join Germany until they found out German had a program of death or servitude for Slavs. So the war is mostly legitimate, but it's a messy legitimacy, made more so by the effective collapse of the League of Nations upon the outbreak of hostilities.
Humanitarian? Keeping in mind that few urging the allied nations to war knew of the Holocaust, the humanitarian objectives of the war have to be seen in the context of what horrors were known to be committed at the outset of war. This also ignores the crimes committed in occupied nations, because by that time the war was underway. Liberation is a humanitarian objective, and it's powerful enough to give the Allied decision to enter WWII a small bit of humanitarian objective. Self-interest, so as to prevent the west (or East, in the case of Russian and China) from ceasing to exist, counts as the primary motive, and means that WWII was not a humanitarian war; it just had a humanitarian component.
All this dry analysis was building to a point, and that is this: Humanitarian War is a new phenomenon, a potentially legal and legitimate one, provided it is undertaken/overseen by the United Nations, and that it has the best interest of the international community, the global commons, and the innocent civilians within a nation at heart. The Persian Gulf War, though a legitimate war, was not humanitarian in much the same way that WWII wasn't humanitarian. NATO bombings in Kosovo/Serbia were humanitarian in objective, but the means and the lack of authorization both detract from that noble purpose. And lastly, the UN/AU mission in Darfur has the potential to be a great humanitarian boon coming from armed force, but it isn't quite a war. This is a new era we have entered, and Humanitarian War has yet to enter as a real thing with form and substance. Currently, it exists as an objective, a justification, and a potential new role for modern militaries. But it is not yet an existing thing.