The first chapter opens with the famous phrase: "Man was born free, and he is everywhere in chains." These "chains" are the constraints placed on the freedom of citizens in modern states. The stated aim of this book is to determine whether there can be legitimate political authority--whether a state can exist that upholds, rather than constrains, liberty.
Rousseau rejects the idea that legitimate political authority is found in nature. The only natural form of authority is the authority a father has over a child, which exists only for the preservation of the child. Political thinkers--particularly Grotius and ##Hobbes##--have asserted that the relationship between ruler and subject is similar to that between father and child: the ruler cares for his subjects and so has unlimited rights over them. This kind of reasoning assumes the natural superiority of rulers over the ruled. Such superiority is perpetuated by force, not by nature, so political authority has no basis in nature.
Nor is legitimate political authority founded on force. The maxim that "might makes right" does not imply that the less strong should be obedient to the strong. If might is the only determinant of right, then people obey rulers not because they should, but because they have no choice. And if they are able to overthrow their ruler, then this also is right since they are exercising their superior might. In such circumstances, there is no political authority; people simply do whatever is within their power.
Rousseau's suggested answer is that legitimate political authority rests on a covenant (a "social contract") forged between the members of society. He has a number of predecessors in theorizing a social contract, including Grotius, who proposes that there is a covenant between the king and his people--a "right of slavery"--where the people agree to surrender their freedom to the king. Grotius is less clear what the people get in return for their freedom. It is not preservation: the king keeps himself fed and contented off the labor of the people, and not the other way around. It is not security: civil peace is of little value if the king makes his people go to war, and desolates the country by stockpiling all its goods for his own consumption. Yet it must be something, because only a lunatic would give up his freedom for nothing, and a covenant made by a lunatic would be void. Besides, even if people were able to surrender their own freedom, they could not justifiably surrender the freedom of their children as well.
It is impossible to surrender one's freedom in a fair exchange. By surrendering their freedom to their ruler, people surrender all their rights, and are no longer in any position to ask for something in return. More importantly, Rousseau links freedom with moral significance: our actions can only be moral if those actions were done freely. In giving up our freedom we give up our morality and our humanity.
Rousseau also objects to the suggestion that prisoners of war could become slaves through an even exchange, where the conqueror spares the life of the vanquished in exchange for that person's freedom. Wars have nothing to do with individuals. Wars are conducted between states for the sake of property. When an enemy surrenders, he ceases to be an enemy, and becomes simply a man.