body: Before anyone asks this is part legal curiosity, part proving for 'loopholes' that I could have villains in a story exploit, I don't need 100% accuracy so much as general guidelines, and any unique situation or known 'loophole' is also interesting.
  
  
  I'm curious about how the US handles travel to other countries to activities crimes that are illegal within the US but legal in the country they travel to. At first I thought that this would be legal, but I know sex tourism at the least is restricted, They actually make us take a training at work about how sex trafficking is bad in case we couldn't figure that one out on our own. 
  
  
  A quick scan online tells me that the sex tourism thing is specific federal law. Outside of sex tourism of individuals under the age of 18 are there other situations where one can be punished for traveling to another country to commit a crime? If so are these specific laws that address only a few unique situations, or is there some general law that addresses many crimes committed by traveling to another country?
  
  
  I can think of a number of theoretical odd situations as fodder for story telling, I'll likely ask a few of them in more detail in later questions depending on the answer in this one. If someone wants to touch briefly on a few odd situations below in their answer I would be interested, but if any of these situations is too complex I'll ask them as a later follow up question.
  
  
  1. how does dual citizenship work in situations where it would be illegal for a US citizen to travel to country X to do activity Y, but the individual in question is not only a US citizen but also a citizen of X?
  2. How much does 'premeditation' apply to these rules? For instance my quick scanning of sex tourism law refers to an individual traveling to a country "with the intent to ...", does that mean if someone travels to a country and only then decides to do an activity it would be legal (ignoring the difficulty of proving it wasn't premeditated)?
  3. Is a non-US citizen within the US (for instance with a visa, or even an illegal alien who lives in the US) still subject to these sort of laws if they leave the US with the intent of doing something illegal within the US and then return?
  
  
  Edit: ...also Id love at least *one* other instance of an activity that would be a crime if someone travels elsewhere to do it. I'm thinking of potential loophole abuse questions I could ask, but I *really* don't want to ask them in context of the sex tourism law. Rather or not it's just a theoretical question to explore legal oddities I really don't like even hypothesizing the sort of situation that leads to someone trying to violate that particular law.
  
  
  
title: If one leaves the US to commit an act illegal in the US but legal in the country they travel to are they guilty of a crime?