The notion of ethics in business can be traced back to the earliest forms of bartering, based on the principle of equal exchange. Countless philosophers and economists have examined the topic, from Aristotle and his concept of justice to Karl Marx's attack on capitalism. But the modern concept of business ethics dates back to the rise of anti-big business protest groups in the United States in the 1970s. The subject gradually became an academic field in its own right, with both philosophical and empirical branches. Then, thanks to government legislation, ethics have been incorporated into businesses, reflected today in corporate social responsibility strategies and codes of conduct. Business ethics is now not only a firmly established academic field, it is something companies realize they need to manage and internalize.