"When you leave Rangers there aren't many teams you would like to go to in Scotland," he said.
"It would be difficult. I wanted a move to the English League and Cardiff City offered the opportunity.
"It's a fresh start for me and Cardiff City are ambitious. They want to make progress and I want to play my part in that."
"It's a big move for me and I have to get it right," said Rae. "I flew down for talks with the manager and chairman Peter Ridsdale.
"They outlined the plans for Cardiff City. Both spoke with genuine enthusiasm and belief.
"I don't know too much about Welsh football because I have spent my whole career in Scotland. But I've asked around and everybody speaks highly of Wales and the city of Cardiff. It had to be Cardiff for me."
Rae was given the No. 3 shirt for the new season.