International law is based on rules made by states for states. States are sovereign and equal in their relations and can thus voluntarily create or accept to abide by legally binding rules, usually in the form of a treaty or convention. By signing and ratifying treaties, states willingly enter into legal, contractual relationships with other state parties to a particular treaty, which observance is normally controlled by the reciprocal effects of non-compliance. The capacity of states to enter into such relationships with other states and to create legally binding rules for themselves, is a result of states' international legal personality, a prerogative attributed to all sovereign states.
In the beginning of the 18th century sovereign states alone were considered to have international legal personality and therefore the only entities with capacity to have rights and obligations under international law. As such, states were (and still are to a large extent) the omnipotent creators of international law which in turn primarily concerned states and their conduct internationally. Individuals, International Organizations (IOs) and other non-state actors (NSAs) were of no concern to international law as they were devoid of international legal personality, which is a prerequisite for the capacity to have international rights and/or obligations.
With globalization however, international law and international relations expanded rapidly with increasing complexities: new technology made the world smaller and more interconnected, new global threats emerged that could not be fought unless with state cooperation, new players emerged at the international forum such as various IOs and NSAs. International law was greatly influenced by this development and shifts in international relations whereby states were no longer the only players on the international arena and thus not the only subjects of international law any longer.
In a landmark case of 1949 the International Court of Justice (ICJ) found that IOs, in that case the United Nations (UN), could indeed have international legal personality and thus have rights and obligations under international law. The ICJ claimed that international legal personality of the UN was derived from the UN Charter and the organization's given mandate and functions, for without it the UN could not perform those tasks it was required to by the UN Charter.
After World War II the Security Council established two international ad hoc tribunals in an attempt to prosecute for war crimes that were committed during the war. The Nurnberg and Tokyo tribunals confirmed that under certain circumstances, individuals can have legal personality under international law and have capacity to have rights and obligations directly under international law, in particular Humanitarian Law (HL) and Human Rights Law (HRL). For the first time in the history of international law, individuals were held accountable for international crimes such as war crimes and crimes against humanity prohibited under customary international law as well as several international conventions.
International liability of individuals has subsequently been confirmed on numerous accounts by various courts such as the United Nations International Criminal Tribunal for the former Yugoslavia and Rwanda, especially established by the UN Security Council to prosecute persons responsible for war crimes, crimes against humanity and genocide under international law.
The procedure for holding individuals internationally responsible for international crimes was finally made permanent with the establishment of the International Criminal Court (ICC), governed by the Rome Statute which entered into force in 2002. The Courts mandate is to prosecute individuals under international law for crimes such as genocide, war crimes and crimes against humanity. Currently there are total of 121 state parties to the Rome Statute.
How about individuals' rights under international law? Can individuals, John and Jane, have rights under international law and moreover seek justice in case their rights are violated?
The treatment of individuals on foreign territory has been regulated by international customary law as well as conventions for decades. Such rules protect states' own citizens when they're on foreign territory, against illegal actions of the foreign state. Thus for example if a citizen from country A would live and do business in the territory of state B and state B would illegally confiscate the assets and business of country A citizen, state A can hold state B responsible under international law before the ICJ (see Diallo case). Whether or not state A drags state B before the ICJ (or other regional or international court) is entirely up to state A without any regard to the wishes of the citizen.
This stems from state sovereignty and the gradually diminishing principle of non-interference in a state's internal affairs. Few decades ago, how a government would treat its own citizens, was an entirely “domestic affair” or an “internal matter” which was by no means of any concern to other sovereign states, left alone the rest of the international community. For decades states' sovereignty veil seemed to be impenetrable until international and regional human rights law acquired global acceptance with unprecedented speed.
The emergence of international human rights law however altered the sanctity of state sovereignty and imposed certain international obligations upon states to respect, protect and fulfil the human rights of all individuals within their territory. International human rights law moreover established “soft” (complaint procedure under the International Covenant on Civil and Political Rights) enforcement mechanisms and regional human rights law went a step further, establishing a hard enforcement mechanism of a human rights court with the capacity to give legally binding judgements on whether or not a state has violated the European Human Rights Convention.