There has not always been a war on drugs the way that there is right now in the United States. In fact, this whole thing can be traced back to President Nixon, who first used the term in 1971. He made a lot of changes to the way that laws worked regarding drugs, including the inclusion of mandatory sentences for drug crimes and the expansion of the agencies that deal with these things.
This is not to say that there were no laws before 1971, as that certainly was not the case. For example, laws relating to opium were passed back in the 1870s, and laws relating to cocaine were passed around the turn of the century, close to 1900. Laws regarding marijuana started to crop up about 10 to 20 years after that.
However, the war on drugs had not been conducted on such a large scale until Nixon decided to make his changes.
Part of the reason for this was because of the drug use in the previous decade. Many young people who were considered to be rebellious were linked to drugs in the 1960s. Because of this increase in use, Nixon took action to counter it.
This trend continued through the 1980s and 1990s. The amount of people being put in jail for drug-related offenses, in Maryland and elsewhere, went up dramatically.
Those who have been accused of drug possession or a similar crime should know exactly how current laws view these things, and they should know what rights they have in a court of law. As is shown, these laws are always changing and being updated, so knowing the most recent ones is of the utmost importance.
Source: Drug Policy, "A Brief History of the Drug War" Sep. 26, 2014