So when you speak of a State's duties to the individual, these are duties that the State can agree to or reject?

First, States agree to certain Treaties, Covenants and Conventions (they all amount to the same thing) which set standards for the treatment by the State of its citizens and call them to account for the efforts they make to implement these standards and answer allegations that may arise. Secondly, even if they do not agree to these treaties, as member States of the United Nations they pledge under the United Nations Charter to promote respect for, and observance of, human rights.

Third, the International Bill of Human Rights and the other human rights conventions make up a body of so called international human rights law. How a government treats its citizens is now the legitimate concern of the international community.

Here is what the Secretary General of the UN, Boutros Boutros-Ghali, said on opening the World Conference on Human Rights in Vienna in 1993,

It is the State that the international community should principally entrust with ensuring the protection of individuals. However, the issue of international action must be raised when States prove unworthy of this task.... and when — far from being protectors of individuals — they become tormentors.... In these circumstances, the international community must take over from the States that fail to fulfil their obligations.

He closed this section of his speech by asking

...whether a State has the right to expect absolute respect from the international community when it is tarnishing the noble concept of sovereignty by openly putting that concept to a use that is rejected by the conscience of the world and by the law. Where sovereignty becomes the ultimate argument put forward by authoritarian regimes to support their undermining of the rights and freedoms of men, women and children, such sovereignty is already condemned by history.