The central defender ended his two year spell at St. Andrew's by moving to Wolves for an undisclosed fee in a deal believed to be worth £6-7 million.
Johnson, who has signed a four year deal, said: "The Carling Cup win was great, great for football, a day I'll never forget. But then again, getting relegated was another day I'll never forget. It was heartbreaking. No-one could believe what went on. There are problems there. Everyone can see what is going on via what has been written."
"He added: I'm not going to get into the financial side of what is happening at Birmingham. All I can say is, I wish them all the best. I made some great friends there. It was a difficult decision but I want to be in the Premier League, that's the end of it.
"Nothing against Birmingham, I had some great times there, the fans were great for me. I gave everything for the club so I hope they can appreciate that. But for me this feels right."
"I'm sure a few people will be disappointed I've not stuck it out but I'm 28 and I want to be in the Premier League for as long as I can. It's been a long road to get here and I don't want it to end."
When asked his targets at Wolves, Johnson said: "I'll keep some in-house but just to make sure this team stays in the league and finishes around mid-table and then kicks on."
Wolves boss Mick McCarthy described Johnson as "a leader" on the pitch after the pair were involved in a verbal touch-line bust-up in the game at St. Andrew's last season.
McCarthy said: "We had a bit of sparring at St. Andrew's. He did have words with me when I was trying to give the ball back to him and he thought I was trying to keep hold of it.
"We did exchange a few pleasantries! Whatever I liked about him before, I liked him even more then so fair dos. That's what I want, commanding players, players who demand things out of themselves and each other and you want vocal players on the pitch."
Source: PA
Source: PA