According to Locke, only governments that can protect and promote the natural rights of man are sovereign. No matter if they can enforce laws. Tyrannies and dictatorships are actually not governments of sovereign nations. Peoples, citizens and even other nations are free to depose these leaders and establish true sovereignty.
You might look to Westphalia, John Locke, and also the principles behind "The Responsibility to Protect."
While you are on track with Hobbes, Rousseau and Locke did the best work on social contract. To that end, governments that don't promote and protect the natural rights of men do not govern sovereignty.
Hobbes noted that men are more apt to suffer than to stir but as noted in the Declaration of Independence "long train[s]" of abuses will lead to the eventual removal of the false sovereign.