Recreational drugs have long been a part of human history. For many ancient societies, recreational use of drugs and religious worship often went together, where mind-altering drugs were seen as a way to communicate with the world of the gods and spirits. Even after the conversion of many societies to Christianity or other monotheistic religions, recreational drugs were still widely used, although not always accepted. However, trade continued to be robust. In the 19th century many naturally occurring drugs began to be derived into new derivatives, such as cocaine, morphine, and heroin. It was only in the 20th century that many countries banned most of the recreational drugs, with the exception of the relatively weaker drugs such as tobacco.