Though freedom is desirable, Rousseau agrees with Montesquieu that it is not possible in every environment. The government of a state does not produce any goods itself, and so must live off the surplus produced by the people. The closer the relationship between the government and the people, the less the taxes levied by the government will hurt the people. Democracy can survive where there is little surplus and monarchy thrives where there is a great surplus. Thus, Rousseau suggests that climate determines government to a great extent. Colder, northern countries have little surplus and can support democracy, while hotter, southern countries have great surplus and support monarchy. In hot climates, people tend to eat less, have more fertile soil, and need fewer people to work the land. Because fewer people are needed, the population will be more spread out, making them easier to govern. All these considerations serve as evidence that monarchical government thrives in hot climates.
Considering the many disputes regarding what makes a good government, Rousseau suggests that the objective and easily calculated factor of population is the best measure. Political associations exist in order to ensure the protection and prosperity of their members. A growing population is a sign of prosperity, and so a sign of good government. Peace, culture, and other factors are nowhere near as important.
The government is inevitably at odds with the sovereign, and the friction between the two can cause the government to degenerate. Either the government will contract--going from democracy to aristocracy or from aristocracy to monarchy--or the state itself will dissolve. The state dissolves into anarchy when the government usurps sovereign power. Such usurpation breaks the social contract so that citizens become free of their social obligations only to be subjected by force.
The friction between government and sovereign is bound to destroy all states eventually. States, like humans, are only mortal, and Rousseau notes that even Sparta and Rome (his two favorites) devolved after a time. The longevity of a state relies on its legislative power: if the laws are upheld for a long time, they become strong with tradition.
Rousseau's peculiar analysis of the effect climate holds on government rests on a certain picture of production and consumption. Each individual needs to consume a certain fixed quantity of goods--food, clothing, etc. However, each individual does not produce these goods equally. While farmers and tailors produce food and clothing, government magistrates produce nothing of the sort. According to Rousseau, then, the farmers and the tailors are responsible not only for producing sufficient food and clothing for themselves, but also producing enough to take care of the government.
Rousseau is a bit vague in his formulation, and we could read this as a simple endorsement of capitalism: magistrates get paid a certain sum for serving in government, and they can use this money to buy food and clothing for themselves. Magistrates get paid taxpayers' money, each citizen paying taxes that are proportional to the profit he makes from whatever business or trade he undertakes.