Yes, this is the entire premise of extradition treaties. If you conspire to commit a crime in a different country, you are potentially able to be sent there to be put on trial. As to whether or not those laws are just is a separate issue.
What's at question here is: Given Assange was never in the US, how has he committed a crime in the US and the answer is that the US has a funny idea jurisdiction.
The country that the individual was in when the crime was committed can certainly handle the issue and not extradite, however, generally these agreements avoid that.
This existed before the internet as well.
https://en.wikipedia.org/wiki/List_of_United_States_extradit...