Two goals in seven minutes from Jesse Lingard and Harry Kane sealed a memorable 2-1 victory over Croatia that means the Three Lions will head to Portugal next June to tackle the hosts, Switzerland and either France or Holland for silverware.
“The players should be very proud of what they have done this year,” said Southgate, whose side pipped Spain to top spot in Group 4 as Croatia were demoted to the second tier.
“We have developed the way we play, but the next stage was winning these big games.
“Over the last two months we have really been able to do that.
“We have had more consistency, but we have got to keep pushing and improving.
“We have beaten three of the top 10 teams in the world and that is really pleasing.
“But there is still a lot more to come.”
Yesterday’s victory partially avenged Croatia’s 2-1 triumph in the World Cup semi-final.
Southgate added: “The World Cup was obviously much bigger, but you have got to look at what the next challenges are. This was a great opportunity to test ourselves against top teams, and we now have another chance to excite our supporters and connect them with the team.
“Next year now looks like an exciting year to look forward to. All the players give their all.”