Be sure to review some of the interviews with people in this sector. Each one has a different story about how they carved a path in this field.
Almost all of them mention opportunities to work in an area they might not have considered, or an opening in a field office that they learned about while overseas, a chance taken that led to new doors being opened. The common threads, though, are persistence, an openness to trying new things, a willingness to do what needs to be done.