system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How come the government was able to ban marijuana with a simple federal law, but banning alcohol required a constitutional amendment?
gpt
At the time of the Eighteenth Amendment, Congress understood that the Interstate Commerce clause did not permit Congress to regulate commerce occuring within a single state. Hence, an amendment to the Constitution was required to abolish it.

Later, with Wickard v. Filburn along with other cases, the Supreme Court effectively wrote the "interstate" part of the clause out, arguing instead that Congress could regulate activity which merely *affected* interstate commerce.

As a result, marijuana regulation and other regulations are now allowed by courts, even if they only impact activity within a single state.