The 48-year-old's departure came at a time when Birmingham were subject to a failed takeover bid from Carson Yeung.
Ironically, this weekend's match will be Yeung's first home fixture since his successful purchase of the club earlier this month.
But Bruce believes the uncertainty surrounding Yeung's first takeover attempt forced him to leave the club.
"I was left in an impossible situation and nowhere to go really," Bruce told BBC Radio Five Live.
"It was becoming a soap opera. [I wanted to know] what we are going to do for the future of the football club. We had just got back up and there was no mention of the team or what we were going to do about the team and about players.
"It was just about the takeover of the club. I was left in a situation where promises were broken. To be fair Mr Sullivan [David Sullivan, the then co-owner] wanted to give me a new contract, then all of a sudden it became an issue with the board.
"It was an ongoing saga. It became impossible to manage. In the end I had to go."
He added: "It became nasty in the end and left a bad taste for what eight years down the line, six as a coach and two as a player - was sad really.
"I think the supporters of Birmingham realised that I had to go for my own self and my own sanity."
Bruce said he had felt particularly let down by comments made by Sullivan after leaving the club.
Sullivan described Bruce's departure to Wigan, which yielded the St Andrew's club £3million in compensation, as good business.
"Whether they [the board] had gone off me I'm not too sure," he said.
"After six years you'd think there would be a little bit of respect. Mr Sullivan's comments that 'We've got £3million and it's the best business the club has ever done' disappointed me.
"I didn't think I deserved that, but there you go it's what happened on the day and subsequently I've never spoken to them since."