The United States has a federal system of government, which means that laws are created at the federal and state level. This allows for flexibility and creativity in policy development because a state can create a law that is different from that at the federal level. Often, these laws can be used as templates to introduce legislation in other states, encouraging innovation.
One example is that of marijuana restrictions. The use and possession of cannabis is illegal under federal law for all purposes, even medicinal, because of the Controlled Substances Act of 1970. However, the law at state level varies greatly. Its medical use is allowed in 31 states, its recreational use in nine (Alaska, California, Colorado, Maine, Massachusetts, Nevada, Oregon, Vermont and Washington), and it is decriminalized in 13 states. The experiments with policy in some states have led to changes in other states, like in the case of California, which was the first state to legalize medical usage in 1996.