system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can South Korea make it illegal for its citizens to smoke weed outside of South Korea?

EDIT: My question isn't "how can they make such a law how dare they", it's more "how is it enforceable in any way".
gpt
They make a law saying they can't smoke weed outside of South Korea, and then they punish the offender upon their return.

FWIW, this is called extraterritorial jurisdiction, and many countries have it.  Most often it is used for things like piracy or terrorism, although sometimes you see it used for other things like sex tourism.  The intent is that if something is illegal, you shouldn't be able to get away with it just because you stepped over an imaginary line on the ground.  Whether these ideas can effectively be enforced is another matter entirely.