Ross Barkley says England's 'future is bright' after witnessing Declan Rice, Callum Hudson-Odoi and Jadon Sancho make their mark on the international stage.
Hudson-Odoi and Rice were granted their Three Lions debuts, while Sancho was also handed his first competitive start against the Czechs.
Barkley also made a huge contribution to England's cause, scoring twice and providing an assist for Michael Keane against Montenegro.
The 25-year-old praised the young trio for their immediate impact at international level, describing their ability as 'frightening'.
"The future is really bright," Barkley told Sky Sports. "You see how the young players have performed and how good they are - Declan Rice, Jadon Sancho and Callum Hudson-Odoi.
"They were frightening in training. It's great to be part of it."
England are now top of Group A on six points, four ahead of Bulgaria and five ahead of Kosovo, with their latest opponents occupying the bottom two spots.
Southgate will be expected to guide his team comfortably towards qualification for the European Championships and Barkley could have a huge role to play.
The Chelsea midfielder felt his display against Montenegro was his best in an England shirt so far, but he is still striving to improve his all-around game.
"It was my best performance for England. I came up with the two goals and had a hand in a couple of the goals - but I felt I could have played better," Barkley added.
"We can all improve. We are not in the game to accept where we are at. We have to improve at club level - and at the international level, there is a lot of room for improvement.
"I never thought I would not play for my country. We all go through difficult spells. But I am just believing in myself now and having confidence."