England, as a general rule. Since the EPL was founded (or maybe more accurately, since the English First Division broke away from the English Football League) in 1992, no English manager has ever won the English Premier League. So zero championships in 33 seasons for English managers in the English first division, as surprising as this might be. And only a small handful have even managed EPL teams in the UCL, since it was re-branded as the Champions League in 1992. English managers don't have a great track record of high-level success outside of England, either. My experience is that as a result, England fans are skeptical that English managers can succeed at the highest level.
England is much more likely to hire an English manager for the national team, for patriotic/nationalistic reasons. But even there, I would say that before Southgate, the best-regarded manager England had during my lifetime was probably a Swede, Sven-Goran Eriksson. And I won't be shocked if England hires a foreigner to replace Southgate.
This skepticism and perception and track record don't help Southgate, IMO. I'll be surprised if he can land a top-level job in the EPL. So maybe the USMNT does have a shot at him, if we want him...