Scientifically, the difference is that hemp plants only contain THC (tetrahydrocannabinol), the psychoactive drug contained in marijuana, not more than 0.3 percent (by dry weight) which is not nearly enough to get a person high. Marijuana usually contains 5 to 20 percent THC, by contrast. Cannabis plants containing 0.3% or less of THC are hemp plants. Cannabis plants are marijuana with more than 0.3 percent THC. Looking at these 2 different forms of cannabis, socially and economically they have very different uses and regulation. More recently, hemp has become a legal substance on a federal level, allowing it to be used in lotions, food, clothing, and much more. Although it is legal and less regulated, farmers still need a license to grow the crop. Cannabis marijuana is much more highly regulated by states and has not been legalized on a federal level. Due to its psychoactive properties, it is highly regulated and highly taxed. 

I think the people in America and any other countries have established that there is a market for Marijuana, whether it be hemp and cannabis, so I think the regulations will change as the market continues to grow. We are a capitalist country that has never shied away from a booming market, no matter the regulations in place. If the demand continues to grow, and farmers continue to see a profitable market, the governmental regulations will definitely begin to shift in order to appease the mass market.