I hate the concept of the Security Council where ONE member can vote down a proposed action before the UN in general can know about it, let alone debate it. Nations with despicable human rights scores nonetheless serve on the UN Human Rights commission.
I do not like the United Nations, they really accomplish very little of any value. Some dictator somewhere violates international law? Why, a UN proclamation will set him straight, and if not, we'll sanction him! If that doesn't work, we'll reiterate our sanctions every odd-numbered day until that dictator reforms! Really, its a useless bit of nonsense.
Look at North Korea. The UN wags its forefinger at them and tells them off for being naughty, and North Korea happily wags a different finger right back. Makes me feel safer knowing the UN is doing its usual stellar job with the more recalcitrant regimes out there.
Their peacekeepers did a bang-up job in Syria, didn't they? They could write a textbook on that operation. They also have a contingent in Haiti, because people on the verge of starvation make ideal soldiers. Disclosure: the US didn't do Haiti any favors, at all, by supporting Duvalier, but I was 7 when he was overthrown, so I don't accept any responsibility for that choice.
The UN often seems like it has zero respect for the rights of individuals, or national borders. All too often, the UN seems to operate as if it is in charge and national governments are subordinate to it, rather than it being little more than an advisory body.
As for NATO...well, every country *is* free to choose what percentage of the GDP they contribute to NATO, and this includes money and material - the "expectation" is 2%. But the money is supposed to go to upkeep and improvement over the member's own military forces that are designated as part of NATO's forces should they be called up. So with the largest military involvement in NATO, the US pays in the most. Iceland *has* no military, so they pay very little into NATO. If Germany or the UK *wanted* to raise their contributions, the US wouldn't argue against it, but the nation would need to increase the section of their military that is designated as available for NATO use, to absorb the extra funding, and then politics gets involved. No politician would want to sign off on (potentially) having more of the military taken away from home defense and deployed by, potentially, foreign commanders not even paid by the same government. That caused Pershing and Haig to lock horns during World War One, and wouldn't sit any better in the modern era.