Always the US Government, since ever. Like over in Switzerland, cannabis was banned in 1951 under pressure from the United States of America. One of the main reasons was that US soldiers, stationed in Germany, went in their free time to Switzerland to smoke marijuana.
But the whole change came with the introduction of cotton in the 20th century. Cotton was much cheaper and easier to process than cannabis. Together with the synthetics emerging at that time, it displaced the hemp products from the market.
At the same time, the state in the US created strict laws to ban cannabis. This is called "prohibition." It was directed primarily against the poor, often colourful population, in which marijuana was widespread.
So thanks USA, again I guess...