Johnson, who left City in a £10 million move last week to return to his native North East, has been called up to the Three Lions' squad for the opening World Cup qualifiers against Moldova and Ukraine.
The 25-year-old admits he was frustrated by a lack of first-team chances at the Etihad but was buoyed by he fact that he was still called up to the national side.
Johnson told The Daily Mirror: "It was difficult, it was tough. I was there or thereabouts with the last manager. He still called me up, apart from going to the Euros.
"But obviously sitting on the bench for any amount of time is going to hamper your chances if someone is playing ahead of you, and doing well week in, week out.
"If you're on the bench and not even playing, then I think it's only right that the other person plays, isn't it? It plays a little bit on your mind.
"The England manager has come out and said he wants his players to be playing regularly, that you can't sit on the bench forever.
"So that's another reason for me to come to Sunderland and hopefully get more games and keep carrying on playing for England. Hopefully I'll be going to the World Cup in Brazil.”
Johnson admitted that missing out on a place in England's Euro 2012 squad this summer made him realise he needed to move on and start playing football regularly again.
He added: "Not going to the Euros was a big thing. I probably already knew at the end of last season that my time would probably be up.
"City are always buying whoever and spending whatever, so there's always going to be someone coming in to take your place, so I owed it myself to move on and get games and try and show everyone what I can do again.
"I started the last game against Italy, hopefully it's looking bright for me now with England and this will be a good move for me and a refreshing new start. It can only get better."