[Laws] “should be in relation to the nature and principle of each government; whether they form it, as may be said of politic laws; or whether they support it, as in the case of civil institutions. They should be in relation to the climate of each country, to the quality of its soil, to its situation and extent, to the principal occupation of the natives, whether husbandmen, huntsmen, or shepherds: they should have relation to the degree of liberty which the constitution will bear; to the religion of the inhabitants, to their inclinations, riches, numbers, commerce, manners, and customs. In fine, they have relations to each other, as also to their origin, to the intent of the legislator, and to the order of things on which they are established; in all of which different lights they ought to be considered. This is what I have undertaken to perform in the following work. These relations I shall examine, since all these together constitute what I call the Spirit of Laws.”

Fast-forwarding to more recent times, the classic An Introduction to Comparative Law by Zweigert & Kötz*** might be a good place to start for those wishing to find out more. The publisher says this about the third edition: “The book first discusses the nature of Comparative Law, its functions, aims, methods and history, and then it surveys the main features of the major legal families of the world. In the second part it provides a model of comparative law in action, comparing, contrasting and evaluating the different approaches and solutions of the major legal systems. As well as offering an excellent grounding in comparative private law, this book is an essential base for further research.”

You may be interested to watch Hein Kötz giving the Eason Weinmann Lecture at Tulane University Law School in 2011 – “Contract Law in Europe and the United States – Legal Unification in the Civil Law and the Common Law”. http://www.law.tulane.edu/tlscenters/eason/index.aspx?id=15657#koetz