Bruce paid tribute to his former Manchester United teammate Roy Keane - who restored the club to the top flight - but explained that the squad Keane left needed to be trimmed to fit in with his vision of how to move the club forward.
"From the start, I was mindful that just two years previously Sunderland had just got out of the Championship," he told SAFC-TV.
"There has to be a big compliment paid to Roy in that respect because he brought the club up and kept it in the Premier League.
"In doing that, for me the squad got a bit too big. We had to do some severe pruning and take big decisions.
"That's what management's about - putting your own stamp on the club and the team."
He added: "I thought as soon as I walked through the door that we needed to strengthen right down the spine of the team.
"You didn't have to be a rocket scientist to work that one out and it resulted in the signings of Darren, Mensah, Turner, Cana and Cattermole.
"Thankfully they've all had good starts to their Sunderland careers."