KG has never been the type to mince his words during interviews, and here's another example to bolster that claim.
Garnett was a guest on the Ringer's Bill Simmon's podcast, where they discussed a myriad of things, including the 2010 NBA playoff run, where the Celtics beat the Lebron led Cavaliers in six games. This series not only became infamous for Lebron's lack of intensity during the series, (or the Delonte West incident), but it was the catalyst for launching Lebron to Miami to form his own big three with Dwayne Wade and Chris Bosh.
During the interview, Simmons posed the question as to whether or not Garnett could break Lebron's spirit in today's game, to which Garnett immediately responded by saying they (Celtics) broke him in 2010:
No doubt, the Celtics played a huge part in James's decision to wanting to take his talents to south beach. During the big three era, the Celtics were widely considered the beast of the east for quite some time. Up until 2012, when the self-proclaimed king claimed the throne and terrorized the conference while playing for both the Miami Heat and his second stint with the Cleveland Cavaliers.