We now know as historic fact, through recent archaeological evidence, that marijuana has been cultivated and used by humans for over 14,000 years. Its origins have been located in Mongolia, in digs dating back to 12,000 BC.
From there, its cultivation and use as both medicine and mood elevator spread east to China, and by 2,000 BC Japan was raising cannabis crops. By 2,000 BC archaeological evidence shows that marijuana was being raised in India and the Near East. Evidence of domestication has been found in Easter Europe also around 2,000 BC, or 4 thousand years ago.
It's arrival as a cultivated crop in Africa and and Western Europe dates around 700 AD - with grass arriving as a crop in England around 1200 AD. South America received marijuana around 1600 AD, and North America as late as 1910. Here's a map that shows how grass migrated from its domesticated origins in Mongolia, outward in all directions:
If you'd like to read more about the history of grass in various world civilizations throughout history, here's a link to a good article that will lead you to a number of additional sources, depending on how deeply you want to dig into this.
What's important to note is that cannabis as an illegal substance is very very new on the planet - and hopefully that negative judgment on the value of marijuana is being removed throughout the world.