U.S. law does follow U.S. citizens around the world, but only in certain circumstances does it apply to conduct abroad. For example, there is a law against U.S. citizens engaging in underage sex tourism abroad. But such laws are the exception. If you, e.g., murder someone in England, the U.S. can't hold you accountable under American law.

Your example is a bad one, because in your example the law is broken by conduct in the U.S. In this case, the splicing of the leased lines happened outside of the U.S.