Say you take an illegal drug in country X, but they don’t find out. Then you go home and they saw pictures of you taking it - is it still illegal since you did it outside of the country?
Which laws are international and which are national? For example, my guess is that drugs are only illegal to use within various nations - and that no one ever gets in trouble via one nation telling another about your drug usage. But what about marriage law. Will one nation go after you for child support if you have two marriages in two different countries?
Most crimes are national. That’s what extradition is for - If I commit a crime in the USA, even one that may not be a crime in the UK (Have sex with a 16yo?) The US authorities *could *apply to have my ass hauled over to the state where I did the deed to be tried. “Could”, because it is probably unlikely.
Almost all criminal law is national in scope (ignoring the various constitutional settlements which give varying levels of authority to sub-national bodies; as far as International law is concerned it is all national law).
Generally speaking, international law is created and applies only as a result of agreements between nation-states and any criminal courts trial and or sanction result from said agreement.
What the OP is talking about here not international law but crimes, offences and disputes which are transnational either partially or in totem.
Drug offences are certainly country wide. There are some substances whose trade internationally on prohibited vide treaty though.
Depending on the circumstances it might be illegal to be have multiple marriages in one jurisdition and you could find yourself prosecuted in that jurisdiction. Child support is a civil claim; civil judgements are enforced in a variety of ways; there might be pre-existing agreements between jurisdictions to execute each others decrees (almost all Commonwealth nations have that agreement) and another common way is to file suit in the jurisdiction you want the decree executed ysing said decree as a cause of action.
Not usually, but e.g. South Korea had a reputation for prosecuting anyone on their soil who was found to have used marijuana, regardless of where they used it (though maybe they’ve stopped now?).
If you commit a crime in Country X, under Country X’s laws, then Country X can always prosecute you, and maybe convict you in absentia, but to arrest you they’ll need the cooperation of wherever you’re currently living*. In some cases, a treaty will obligate your country to extradite for certain crimes. The absence of a treaty doesn’t guarantee that they won’t extradite, though (e.g., the Pirate Bay guy from Cambodia).
There are also cases where an action that you took in Country X is still a crime in Country Y. That’s universal or extraterritorial jurisdiction, and it usually applies only to the most serious and/or conveniently portable crimes, like wartime atrocities, or tourism for the purpose of child prostitution.
In the US, there have been some laws created specifically regarding conduct in foreign countries (e.g. sex tourism). Aside from those, I’d expect you to have a very strong case challenging the jurisdiction of any prosecuting court (assuming you’re a US citizen being charged in US court for actions outside the US).
I believe that is the opposite of what the OP is asking. I believe he’s asking about, for example, an American taking a trip to Amsterdam and smoking a little pot, then does he risk prosecution when he gets back home?
I believe the United States government maintains that its Federal laws apply to all American citizens no matter where in the world they may be, unless that conflicts with a local law.
So if you go to Switzerland or Mozambique or Outer Mongolia and there harass a whale, you can be prosecuted for that. I would assume that they don’t try to extradite you but instead wait for you to return to American territory. A long time ago, I read an article somewhere that specifically mentioned that the United States government would enforce the Marine Mammal Protection Act this way.
One point to be made is that the extradition treaties that Canada has with other countres requires that the act be criminal in both countries. That was the ostensible reason Canada would not extradite draft dodgers; Canada had no draft. I assume the principle is universal.
It’s not the “ostensible” reason - it was the reason. Canada had no legal authority to deport someone, if they were in the country legally and had not committed an offence in Canada.
Contrast that to the deserters from the US armed forces who came north to Canada during the Iraq war. Canada did deport or extradite those one because Canada, like the US, does have an offence of military desertion. The principle of double criminality, which is a keystone of extradition treaties, was met.
Having sex with a 16 y/o is actually one of the few offences where extraterritoriality applies. (I think joining certain banned poloitical movements, like ISIS, also qualifies). There was a law passed in the early 2000s to that effect.
American 18-20 year olds routinely go to Montreal or Mexico to break the U.S. drinking laws, and as long as they aren’t under the influence when they return, I don’t think there’s much the US government can do about it.