Pep rallies, appearances on the house network, and plenty of excitement ushered in a new era for the Southeastern Conference on Monday.

July 1 was Expansion Day in college sports, when the start of the new athletic year began and 21 Division I schools across the country switched conferences. Texas and Oklahoma were among that number as they officially left the Big 12 to join the SEC.

“We had 2,000 people here at midnight to start the day, and then a few hours later we’re waking up in Tulsa, we’re waking up in Oklahoma City, we’re waking up all over Sooner Nation,” Oklahoma director of athletics Joe Castiglione said during an interview on the SEC Network. “It has been the adrenaline rush of all adrenaline rushes because we’ve been almost holding back a little. We cannot wait to get it started.”

Although conference realignment has been a constant in college sports for more than a decade, this might be the most turbulent summer yet.

The Pac-12 shut down as of midnight Monday and its members scattered to other leagues. Four joined the Big Ten, four more went to the Big 12, and two to the Atlantic Coast Conference. Only Oregon State and Washington State remained, keeping the league’s trademarks while forming at least a temporary alliance with the Mountain West Conference.

The SEC, meanwhile, poached the two charter members of the Big 12. The move was announced in July 2021, but Texas and Oklahoma remained in the Big 12 for another two seasons because of contractual obligations. The universities reached an agreement with the Big 12 that allowed them to join the SEC a year earlier than planned.

SEC commissioner Greg Sankey said the decision for the league to pursue Texas and Oklahoma were with an eye on the rapidly changing landscape in college athletics.

“My view was that things in college athletics were going to change. In 2021 my belief was conference membership was not going to remain static. I had told our presidents back in 2015 that change was likely around the Big 12 around ‘22 or ‘23 because of TV contracts. And so we moved early,” Sankey said on the SEC Network. “I think what you’ve seen in the intervening years happening around us, not to us, not really just because of us but around us, has indicated it was the right decision on the behalf of our members.”

The addition of Texas and Oklahoma marks the SEC’s third expansion over the past 30-plus years. Arkansas and South Carolina joined in 1992, and Texas A&M and Missouri — also founding members of the Big 12 — in 2012.

Adding the Big 12’s two most powerful members will add remarkable competitive depth to an already powerful SEC. Texas reached the College Football Playoff semifinals last season, and Oklahoma has won more conference football championships (50) than any other FBS program.

The two schools are elite in other sports as well. Texas is a perennial baseball power, and Oklahoma has won four consecutive national championships in softball.

“This will be the most unforgiving league there is in America. That goes without saying. This is a league that is very, very hard top to bottom and the margin for error is very small. It’s thin air, if you will,” Oklahoma football head coach Brent Venables said. “But that’s what this program has been about for a long time. We’re running toward the SEC with great expectations and excitement. This will be a launching point for this program moving forward.”