International law recognizes the fact that the international community is made up of various sovereign states whose individual sovereignty and political freedom should be unwaveringly defended and respected. It is for this purpose that the doctrine of non-interference and total respect for the sovereignty of other internationally recognized states forms the essence of the United Nations Charter ( Although there are other sources of international law, the UN Charter is widely regarded as a sort of the international community's Constitution). Article 2(4) of the Charter expressly states that “[A]ll members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations". The Charter only allows interference in one exceptional circumstance: self-defence (Article 51).
These principles were ostensibly for every state actor to observe. But in practice the big boys are definitely above them and have showed contempt at every opportunity they get all while expecting the other guys lower in the food chain to fully adhere. If a smaller country deviates from this norm, a full "international" outcry complete with concomitant sanctions is sure to follow. But let one USA and one Britain invade and blatantly violate the core principle of international law by invading a number of sovereign states without a justified cause, then well, it is not a big deal. They simply don't give a damn.
