Democratic and aristocratic states are not in their own nature free. Political liberty is to be found only in moderate governments; and even in these it is not always found. It is there only when there is no abuse of power.
Montesquieu shows he is a realist about human nature: giving one person or a small group too much power and trusting them to do the right thing or trusting in a particular form of government is naïve and a recipe for disaster. The only way to avoid abuse of power is to make sure that no one person gets too much power. Power must be distributed broadly for there to be a secure and just state.
Again, there is no liberty, if the judiciary power be not separated from the legislative and executive. Were it joined with the legislative, the life and liberty of the subject would be exposed to arbitrary control; for the judge would be then the legislator. Were it joined to the executive power, the judge might behave with violence and oppression.
In book XI, Montesquieu discusses the importance of the separation of the powers of the state so that no one individual or group of people can seize too much control. This concept had an enormous impact on the Founding Fathers's structuring of the United States government: the three branches of government—executive, legislative, and judicial—are designed to be in tension with each other. Each one is supposed to keep the other two in check.
There is no greater tyranny than that which is perpetrated under the shield of the law and in the name of justice.
Once again, Montesquieu cuts to the chase: laws mean nothing unless they are just laws. Just laws only arise when no one person or group has too much power. We can look to Nazi Germany as an example of this principle: Many of the human rights abuses perpetrated by the Nazis were perfectly legal under the Nazi government—in fact, the Nazis were fairly scrupulous about legality and about making a show of "justice" in the their court system, but their laws were unjust by any reasonable moral standard.
When the savages of Louisiana are desirous of fruit, they cut the tree to the root and gather the fruit. This is an emblem of despotic government.
Montesquieu was a critic of the power of the monarchy in France in his time period and saw that people with too much power take what they want and don't care about the consequences or the future.