Legal Question in Business Law in California

Re: US Common Law

The main reason is that at the time the United States was formed (Declaration of Independence in 1776 and victory in Revolutionary War followed by adoption of the Constitution in the following decade), most of the population of the original states was English, formerly English or of English ancestry. The legal system of England was called the "common law" and that system was in place already and well understood by the colonists.

We have one state (Louisiana) which has such a strong French heritage (the U.S. bought Louisiana and other largely unsettled territory from France in 1804, the Louisiana Purchase) that it never gave up French law, which is known as "civil law" in distinction from common law. All the other states use the English common law, including those originally settled by Spain or Mexico such as New Mexico, Florida and California, or by Russia (Alaska).

So, we are a common-law country (largely) for much the same reasons that our predominant and official language is English.