Two weeks ago, George Kliavkoff, the commissioner of the Pac-12 Conference, stood on a Las Vegas nightclub stage and — after a video montage celebrating the league’s rich history of star quarterbacks that runs to the present — confidently proclaimed a bright future.

A new media rights deal would be announced “in the near future,” he said at the conference’s football media day. The impending agreement would lock in 10 schools and pave the way for expansion, eliminating the uncertainty that had hovered over the Pac-12 since the University of Southern California and U.C.L.A. had bolted for the Big Ten last summer.

Kliavkoff waved off concerns about the Big 12 poaching his schools.

“The truth is we have bigger fish to fry,” Kliavkoff said.

By the end of Friday, the Pac-12 was cooked.

A week after Colorado jumped to the Big 12, two of the conference’s remaining cornerstones, Oregon and Washington, refused to agree to a proposed television contract they deemed insufficient and instead headed to the Big Ten. Later, Arizona leapt to the Big 12, taking Arizona State and Utah with them.

By nightfall, all that was left of the Pac-12 were Stanford, California, Washington State, Oregon State and the memories of a century-old alliance.

“The old question — how long would it take TV money to destroy college football? Maybe we’re here. Maybe we’re here,” Washington State football Coach Jake Dickert told reporters after his team’s practice on Thursday, when the rumblings of a collapse gathered momentum. “To think even remotely, five years ago, the Pac-12 would be in this position, it’s unthinkable to think that we’re here today.”

It might have been unthinkable just a few days ago. There was little interest in the Big Ten in expansion — until earlier this week, when it looked as if Arizona was itching to leave. And if Oregon and Washington, so unhappy with a Pac-12 media deal that centered on Apple TV, were coming hat in hand, willing to take a reduced offer …

The Big Ten cobbled together a proposal, the Northwest schools nodded yes, and after a quick meeting of the Big Ten’s council of presidents and chancellors on Friday evening, the conference announced that a year from now, it would comprise 18 teams.

The Pac-12 has billed itself as the Conference of Champions, which is hardly hyperbole. Stanford, U.C.L.A. and U.S.C. have each won at least twice as many national championships as any other school. Cal and Oregon rank among the top 15.

But the increasingly big business of college sports is driven, more than ever, by football’s television lucre. Everything else is just details.

Schools in the Big Ten, like Ohio State and Michigan, and those in the Southeastern Conference, like Georgia and Louisiana State, reap enough money solely from football television rights — upwards of $50 million — to cover the entire athletic budget at a school like Florida Atlantic, which reached the Final Four this year in men’s basketball.

Hundreds of millions more from television rights are distributed to the top conferences from the six College Football Playoff bowls.

Those windfalls, though, are mostly plowed back into football in the form of ballooning staffs, ever more opulent facilities and amenities that service the athletes, who do not share the revenue directly but who take on a greater burden of conference realignment with coast-to-coast travel.

That travel burden will be shared by athletes in the non-revenue sports, like tennis players at Arizona taking trips to Central Florida and West Virginia, and lacrosse players at Oregon going to Rutgers and Penn State.

The Pac-12’s demise, as quickly as it arrived, was years in the making.

A little more than a decade ago, the conference’s commissioner, Larry Scott, was hailed as a visionary — a college sports outsider who landed a 12-year, $2.7 billion media deal after adding Colorado and Utah that more than tripled the conference’s rights fees and placed it ahead of every other conference.

But Scott’s insistence on launching the Pac-12 Network without ESPN or Fox as a partner turned into a colossal failure because the conference had no leverage with cable distributors. Thus, many of them refused to meet the Pac-12’s asking price and left the network with far fewer viewers — and far less revenue — than other conference networks.

Scott was forced out and replaced by Kliavkoff, a former MGM executive, two years ago. But by then, the conference’s revenue gap, and U.C.L.A.’s $100 million budget shortfall, made the Los Angeles schools an inviting target for the Big Ten, whose pursuit was done hand-in-hand with Fox, its business partner.

The Pac-12, whose media rights deal expires after the 2023 season, immediately began negotiations for a new agreement after U.S.C. and U.C.L.A. announced their departures last summer. But the Big 12 jumped ahead, reaching an early extension with Fox in October that would generate an average payout of $31.7 million per school.

That deal, considerably less than those of the Big Ten and the SEC, convinced the Pac-12 to downgrade its expectations. Kliavkoff told the University of California Regents, when he was encouraging them to block U.C.L.A.’s move to the Big Ten, that the Pac-12 was lowering its estimates by 10 percent.

Even worse for the Pac-12, its list of potential partners had dwindled by then. By November, Fox had agreements with the Big Ten (as did CBS and NBC) and the Big 12, and ESPN had the SEC and A.C.C. Meanwhile, cord cutting had roiled the cable industry, even cooling ESPN’s voracious appetite for college football.

It was around then that Amazon and Apple became serious bidders.

But Kliavkoff’s inability to close a deal — expectations of January gave way to April, which gave way to June — tested the patience and the confidence that the terms, which were a tightly held secret, would be satisfactory.

“Today’s news is incredibly disappointing for student-athletes, fans, alumni and staff of the Pac-12,” the conference said late Friday in a statement. “We remain focused on securing the best possible future for each of our member universities.”

Ultimately, the Apple deal that was laid out this week guaranteed schools more than $20 million with revenue sharing from subscriptions that could push each school’s cut into the $30 million range, and perhaps higher, according to a person familiar with the proposal.

Though streaming appears to be the future, there were concerns about committing so wholeheartedly to a medium that older fans may not understand. And would recruits even see the product?

The proposal’s structure mirrored Apple’s 10-year, $250-million deal with Major League Soccer, which is required to reinvest some of that money in its broadcasts, but whose luring of Lionel Messi could leave the league in a strong position to reap additional revenue from subscription sales.

Of course, there is an international appeal of soccer — and Messi — that might drive Apple TV subscriptions around the world in a way that Oregon State football just can’t match.