Great britian entered world war 1 primarly because

What federal law makes marijuana illegal i know it's a schedule 1 drug but what law specifically gives the federal government the ability to arrest or fine you over marijuana i have only been able to find info on the scheduling of the drug but it never says this or that is illegal it just says that it's a schedule 1 drug i need the wording exactly my english teacher says that if i don't have it my paper is null and void