The case law system first appeared in Britain and in the Middle Ages. The British rulers at that time urgently needed to create a common law applicable to the whole country. It has no ready-made laws to learn from. It was not until the12nd century that the western European continent began to study Roman law, but at that time Britain had highly centralized judicial power represented by the royal courts. It is in this historical background that such a tradition has formed: major judgments are published regularly, and judges refer to previous judgments as the basis when making judgments. This is the reason why case law was formed at the beginning, which is convenient for people to understand and for judges to judge cases. The American legal system is inherited from Britain, so it also retains the characteristics of case law.

Reasons for the formation of written law: After 12 century, Roman law revived, and the study of Roman law combined with the actual needs of society and became an authoritative supplementary law in continental countries of Western Europe. After reform and development, Roman law has become the common law in Europe, with common characteristics and legal traditions, thus laying the foundation of the civil law system.

With the victory of the bourgeois revolution and the establishment and consolidation of the capitalist system in many western European countries, the legal systems of these countries have further developed with the development of capitalist economy, politics and culture and the exchanges between countries. First of all, in France, under the impetus of bourgeois revolution, under the guidance of classical natural law and rationalism, and under the direct influence of Roman law, a model of formulating a complete statutory law system was created. The Code of France has become a model for European countries to establish their own legal systems, marking the establishment of a modern continental law system model. Subsequently, Germany enacted a series of codes on the basis of inheriting Roman law and absorbing French legislative experience. The German Code has become a typical representative of the era when capitalism developed from a free economy to a monopoly economy.

Because the civil law represented by France and Germany has adapted to the needs of the whole capitalist society, and because it adopts a strict written form and is easy to spread, the civil law system has crossed Europe and spread all over the world since the19th century and the 20th century.

These should be the contents of western legal history.