Your first offers will be based solely on the prestige of the league you're in and the team you manage. Success will bring larger/better offers. You can manage an MLS team and get Austria, Hungary level offers. I've managed Everton and gotten Iceland and Greece. If you manage one of the big clubs you'll get Brazil, Spain, Argentina, etc.
If you managed a mid/low level Premier League team and win the title that can help, too.
I feel like the nationality of your manager was more of a factor when when had the EA Catalogue and one of the items you could unlock and use was getting an international management offer from your home country.