As you can see from this pictorial history, hemp was a vital part of American colonial life, and carried over into early US history. Probably, the most cited example is George Washington who grew hemp for commercial use, as did many plantation owners. Hemp was a viable cash crop, until cotton came to replace it in the 19th century, with the advent of cotton gin. Hemp was used in everything from rope, to clothes to ship sails and even the pages of the Bible. Jefferson also grew hemp at Monticello, primarily for use on his plantation. Here's a partial list of his personal records noting the use of hemp.
However the cultivation of cannabis sativa as a narcotic changed the way many persons looked at the plant. At first the US tried to regulate the substance with a "Marihuana Tax Act" in 1937, but it generated very little revenue, and anxiety grew over the recreational use of the drug, ultimately leading it to be treated as a controlled substance and subject to arrests and convictions. Today, marijuana possession amounts to nearly half of all drug possession arrests, with one occurring every 42 seconds, according to FBI records.
Hemp production has likewise suffered, as most states weren't willing to accept the commercial and medicinal uses of the plant. Recently, Colorado harvested its first hemp crop in more than 60 years, indicating a major shift in federal policy. Given its many uses, one would think the next step is to actively encourage its cultivation as a sustainable form of production.
Of course there are many conspiracy theories as to why hemp cultivation has been kept dormant for so long, especially when it is so popular in so many other parts of the world. Everyone from private prison corporations to pharmaceutical companies have been held accountable for these seemingly unjust laws. However, the AMA was against the tax act in 1937 and continues to encourage the federal government to relax restrictions on the drug so that it can be more thoroughly studied, namely for its medicinal potential.
It seems in this day and age of citing Founding Fathers on everything from the right to bear arms to the freedom to express one's religion, it is fair to note their support of hemp production and the fact that hemp made up the majority of paper products at the time of the writing of the Declaration of Independence, with Jefferson writing the first draft on hemp paper. Too bad they didn't add a watermark "In Hemp We Trust."