Until the founding of the United Nations, the planet was essentially in a state of anarchy, albeit an anarchy of sovereign states. “Anarchy” is the name for when a territory is not governed. Prior to the UN there was no agreed-upon power that could claim to govern the behavior of nations (enact laws, impose sanctions). A political power (in the form of a nation-state, an empire, a colony) has sovereignty when it can govern with impunity (without fear of punishment). Current international law has encroached the sovereignty of nations insofar as the global community has the right to intervene in the governance of people when the rights of the people are being violated in a grievous manner. So, when a national government engages in genocide, the UN has assumed the right to intervene.
The extent, or boundaries of a state’s sovereignty has historically been in flux, but in most parts of the world a nation claims to own 12 miles above its territory, though in practice nations claim more, placing the boundary in the outer atmosphere or in outer space. The Air Traffic Control of different countries may set different standards. The same reaches of sovereignty in the air is claimed by nations of the sea: a nation is recognized as owning 12 miles off its shore. Once you travel beyond the 12 mile point, you are in open sea, owned by no on (res nullius). However, if the Law of the Sea Treaty is ever ratified, the international “open sea” would become public property (res publica). Hugo Grotius, a Dutch philosopher of law, argued strenuously for the freedom of the high seas, though he also sought to secure international law based on his view of natural law. For Grotius, then, under the heading of universal jurisdiction you can still commit crimes at sea and others can take it upon themselves to punish you. And yet, until a world court was established, it was difficult to impose universal sanctions.