LeBron James has left one would-be contender after another in the East in tatters as he’s ruled the conference for over a decade. (Ken Blaze/USA TODAY)

The Toronto Raptors just completed easily the most successful three-year stretch in franchise history — and then fired their coach.

Why? Because Dwane Casey failed in the same way that virtually every Eastern Conference coach has over the past dozen seasons: He failed to stop LeBron James in the playoffs. And as James nears the end of his 15th season, the gap between him and the rest of the East has arguably never felt greater.

“I’m definitely not a one-man army,” James told reporters Friday, in response to a question about him being responsible for Casey’s firing.

Yet over the past dozen years, that’s essentially what he has been to the list of potential contenders in the Eastern Conference — and a nearly indestructible one at that. Having reached the NBA Finals in eight of the past 11 years, he will attempt to do so once again when he leads his Cleveland Cavaliers into the conference finals, which begin Sunday afternoon in Boston.

Since first reaching the postseason in the 2005-06 season — his third year in the league — James is 31-4 in playoff series against Eastern Conference foes. His four losses came against great teams: the 64-win Detroit Pistons in 2006; the 66-win Boston Celtics in 2008; the 59-win Orlando Magic in 2009; and the 56-win Celtics in 2010.

Otherwise, James has rolled through the East, dismantling one franchise after another. Entering these Eastern Conference finals, he has knocked seven franchises out of the playoffs at least three times: the Indiana Pacers (five), the Celtics and Chicago Bulls (four), and the Raptors, Pistons, Atlanta Hawks and Washington Wizards (three).

Just as losing repeatedly to James and the Cavaliers cost Casey his job — and could lead to bigger changes in Toronto — that list of teams is full of coaches and cores that were broken up, in part, because of repeated failures to defeat James.

The Gilbert Arenas-led Wizards lost three times in a row to the Cavaliers from 2006-08; for a variety of reasons, they missed the playoffs the next five years — and returned with a totally new core after changing coaches twice. The 2011 Celtics lost to the newly formed Miami Heat juggernaut in 2011 and ’12; a year later, Doc Rivers, the only coach to beat James in the East playoffs twice, was gone, as was Boston’s Big Three of Paul Pierce, Kevin Garnett and Ray Allen. Tom Thibodeau’s Bulls lost to James three times — in 2011, 2013 and 2015 — and have since overhauled their teams. Same goes for the Pacers, who have seen their season end against James five of the past seven years, and the Hawks, who were swept by James in 2015 (when they won 60 games) and ’16 before blowing up their roster.

Time and again, James has dashed the hopes and dreams of teams hoping to compete for a championship in the Eastern Conference, derailing the best-laid plans of one franchise after another. Through it all, he has remained unbroken and unassailable, looking as utterly dominant physically as he ever has while growing ever more ruthless from a mental standpoint.

One contender after another has come for his throne — the trio of Celtics’ stars, Derrick Rose and Joakim Noah, Paul George and David West, Al Horford and Paul Millsap, and now DeMar DeRozan and Kyle Lowry — all thinking they had a chance to be the first to take him down.

All have failed.

“Hard to say one thing,” DeRozan said after losing Game 4 Monday. “The last three years have been rough for us, competing against this team. Maybe they’ve just got our number. Things just don’t go right for us. Whatever it is . . . it could be a lot of things. All I know is the last three years, they have been the reason we haven’t advanced.

“For whatever that is, I couldn’t sit up here and tell you one specific thing.”

No offense to DeRozan, but there is, very clearly, one specific thing that has stood in Toronto’s way, just as it has for every Eastern Conference team this decade.

That would be James, the one-man wrecking crew who has laid waste to every potential challenger over the past seven years — and, over the next two weeks, will aim to increase that number to eight.

Standing in the way will be a Celtics team that has surprised many observers by weathering the injury losses of Gordon Hayward and Kyrie Irving behind the accelerated  development of young players such as Jayson Tatum, Terry Rozier and Marcus Smart and the stabilizing play of Al Horford.

Will that be enough to dethrone James? Most prognosticators don’t think so.

“I’ve been fortunate to play with two great franchises in my career and played with some really, really good players,” James told reporters Friday. “We’ve just had some success in the postseason . . . I’ve had a lot of success in the postseason.

“Probably within the last five years, I bet [the Raptors have] improved in winning percentage every single year. But I guess their front office wants playoff success. That’s what it boils down to, I guess.”

As long as James is playing in the Eastern Conference, good luck to the Raptors — and everyone else — hoping to accomplish that.

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