Hemp was grown around Champaign Illinois during WW II. The Students at the U Of IL found that there was a lot still growing wild there at the ends of fields. Big bust by DEA in the late 60's.
It still grows today in ditches all over western Illinois.
Ironically, widespread industrial hemp growing might make, in the long term, outdoor growing of recreational marijuana much more difficult.
For quality marijuana, keeping the female cannibis plants from getting pollinated is very important. Cannibis is a wind pollinated plant. If there are large fields of hemp growing everywhere any recreational plant outdoors could easily get pollinated by hemp pollen.
Future generations could also decline in quality for the same reason.