My point above, Giraffe, was that although all nations may be expected (by the UN) to follow the UN rules – in actual fact they rarely do so. The vast majority of international wars since the founding of the UN have been done by member states without permission.
Note please that the UN is not synomous with “international law”. The latter existed before the UN and will continue to exist if the UN ceases to.
The funny thing about the US is it insists that everybody should follow international laws if doing so behooves them. As an example, the PRC has amended their “Ocean Law” to prohibit anybody spying in the 200km economic zone. The US became livid.
There is such a thing as international law and it does have extranational powers as certain countries (including the US) are bound over to enforce it and seek out those responsible for violations. Yes it is a series of treaties, but don’t let that fool you into thinking it doesn’t make up a body of laws.
However all laws, even national laws are nothing more than a set of agreements between people and they rely on the effectiveness of it’s enforcement and enforcing it on large nations such as the US has been a problem (though Henry Kissinger is still likely to be arrested should he ever leave the US).
Another thing is, just because there is no UN resolution does not make a war illegal under international law, all countries have a right to defend themselves and their interests (up to a certain etent), however fighting expansionist wars or warmongering are illegal.
International law is generally regarded as very weak because it is so complex to get into, needing the treaties signed and ratified (in many cases, a treaty is signed but not ratified, or the signature later revoked - the US recently did this with the IC), generally with each country exempting themselves from different parts of the treaties… and then the question is enforcement. With UN treaties, the enforcing party is the UN, which often is stuck with shaking a finger and saying “bad country.”
For instance, while both the United States and the Soviet Union ratified the Universal Declaration of Human Rights, (IIRC) the US opted out of the International Covenant on Economic, Social, and Cultural rights, while the Soviets opted out of the International Covenant on Civil and Political Rights. Additionally, the US operates capital punishment, in violation of the UDHR (not to mention a number of other points in it that I won’t get into). The UDHR is largely an idealistic piece without much legal force, vague wording, etc, but it carries the spirit of what the UN was established to safeguard.
So there IS international law - it is just largely vague and formal, without a terrible amount of enforcement behind it.
1948 Israeli War of Independence, where seven Arab countries invaded Israel, not only without UN permission, but in violation of a UN resolution.
1956 Sinai Campaign, where Egypt kicked out UN peacekeepers as a prelude to war with Israel, who pre-emptively (with British and possibly French backing) kicked Egyptian butt. No UN permission there for anybody – not that Israel needed it, that was self-defense.
1967 Six-Day War, where Egypt (and possibly Jordan and Syria) kicked out UN peacekeepers as a prelude to war with Israel, who pre-emptively kicked major Egyptian, Jordanian, and Syrian butt. No UN permission there for anybody – not that Israel needed it, that was self-defense. (Notice a trend?)
1973 Yom Kippur War, where several Arab countries (probably including some or all of Egypt, Jordan, and Syria, possibly including others) invaded Israel, who after a few very close days pulled it together and kicked major Arab butt. No UN permission there for the invaders.
And to provide some balance… mid-1980s, where Israel invaded southern Lebanon to force out assorted terrorist strongholds. No UN permission there, either.