Inspired by this thread about a tribe known as the Sentinelese. I really can’t think of any. There seems to ALWAYS be other issues, economic, political or military, in the background regardless of what gets announced in the press.
The classic example of when we (the international community) should have acted but didn’t is Rwanda. That situation inspired the “Responsibility to Protect” doctrine. But AFAIK, it has never been used as the sole reason for intervention.
Were there other issues in play for the NATO interventions in Bosnia and later Kosovo? I don’t know much about them but they were ostensibly about human rights.
US invasion of Somalia.
A few. 
The Balkans are a traditional smuggling route, both goods and trafficking in persons, into the rest of Europe before during, and after the civil war. During the civil war rule of law was obviously at it’s weakest. That presented greater challenges to the rest of Europe dealing both with organized crime and their extremist groups.
There was a significant refugee crisis as a result of the ethnic cleansing. Besides the humanitarian issue, that cost money in the rest of Europe.
Yugoslavia had a bigger piece of legal trade with Europe than most of Eastern Europe since it wasn’t aligned with the Warsaw Pact. Bosnia was one of it’s main industrial and mining regions. A lengthy and brutal civil war is not generally good for maintaining the production of international trade goods.
In the 80s Yugoslavia’s economy went through a sustained bad period and they took significant IMF loans. It’s hard to pay back loans (or even assign responsibility for portions of them to breakaway entities) when a civil war is raging.
No, IMO the US did this to clean out the pirates and protect international shipping routes.
I’m personally skeptical that you can ever prove that in the positive. Pure unvarnished altruism practically doesn’t exist in the realm of international geopolitics. But I’d welcome counter-examples, if they can survive examination, so I can maybe restore just a little bit of faith in people.
Had Somali piracy even really got going when the U.S. intervened, though? The intervention started at the end of George H.W. Bush’s presidency, and I don’t get the impression that Somalia-based piracy became a significant problem until over a decade later.
What about the US invasion of Haiti in 1994? Or was that to combat drug smuggling under the new regime?
You folk are correct and I was wrong. I confused the timing of the invasion with that of the height of Somali piracy. That’s not to say I believe Bush told the whole truth of what we were doing there.
Upon a cursory look, it appears we may have intervened to protect western aid workers who were trying to distribute supplies to the locals, which is not the same as protecting the locals. I’ll have to look into this more closely.
You can attribute mercenary motives to any humanitarian war, and you can attribute humanitarian motives to any mercenary war.
This is true, though I don’t mean to suggest that every war is a mercenary war. Only that I don’t know of any wars that were fought exclusively to protect the human rights of people in the invaded country.
How about NATO’s 1999 bombing campaign in Yugoslavia?
War/ military intervention is always about a Nations interests. No other reason. They may state other interests, but it is always to extend their own interests, spheres of influence, or retain a balance of power or dominance.
A classic case in the UK in the Great War. One of the reasons given for the declaration of war on Germany was “poor little Belgium”. It was more like Britain did not want a Europe dominated by germany.
A government is never a monolithic entity. It’s comprised of many powerful individuals, each of whom has their own agenda. If the President wants to fight a war for Reason A, the cabinet for Reason B, the National Security Council for Reason C and the Pentagon for Reason D, what was the reason for the war - A, B, C or D?
Generally no. The main reason is that invading, conquering and occupying a country typically results in a lot of death, destruction and human rights violations, even if done under the best intentions.
First that comes to mind is UK in Sierra Leone:
The North fighting a war with the south to end slavery.
Vietnam invaded Cambodia effectively ending the killing fields. However that was just a byproduct of other reasons.
The US cut off trade with Japan over Nanking and other atrocities in China which lead to war.
Vietnam invaded Cambodia not out of humanitarian reasons, which the OP is looking for, but because the Khmer Rouge army kept making large incursions across the border into Vietnam. One especially infamous incident was their massacre of all but two of the 3157 people living in the border town of Ba Chuc.