Nothing brings out the inherent restlessness of the New York Yankees quite like the Boston Red Sox. The teams are rivals, yes, but that only begins to describe the connection. Their relationship exists on a different plane, almost symbiotic, where in order for one to reach its apex the other must be there, too, supplying the necessary fuel.

When the Red Sox romped to their fourth World Series championship in a decade and a half this October, the incentive for the Yankees to avoid little brotherhood after a century of playing big, bad bully only grew. And while New York may well have endeavored to trade for Seattle ace James Paxton even without another Boston title, the impetus to do so was clear in the words of Yankees owner Hal Steinbrenner and, on Monday, the actions of general manager Brian Cashman.

New York’s acquisition of Paxton for three prospects – the highly regarded left-hander Justus Sheffield, pitcher Erik Swanson and outfielder Dom Thompson-Williams – made what was long assumed patently obvious: The Yankees are not going to sit by idly, not with the stunning core they’ve assembled, not as Boston pops bottles and racks up half-a-million-dollar bar bills.

We’re the New York freaking Yankees, they said Monday. Come at us.

And rest assured, the baseball world will target them as it has since the Yankees planted their flags as the glory franchise of the sport and won 27 championships along the way. However much mutual respect there may be – and even as the Yankees rank among the top-five teams annually in spending, the esteem for Cashman and his lieutenants, and how they’ve gone about building this team, is palpable – nothing satisfies the other 29 teams more than watching the Yankees, their pinstripes and their monetary printing press fail.

The deal for the 30-year-old Paxton unequivocally makes them better today. Remember, they won 100 games last season with Sonny Gray, Domingo German, Lance Lynn, Luis Cessa and Jonathan Loaisiga making more than a third of the team’s starts. Getting more pitching was their offseason mandate, and even with Paxton, sources said, it remains a priority.

Here’s what Paxton is: a No. 1-caliber starter when healthy. The caveat there is an important one to note, though, because just once in his five seasons with the Mariners did Paxton reach 160 innings. His career-high 160 1/3 came last year, when he spent time on the disabled list with a back issue. His ability to stay healthy hampered the return Seattle could get for a pitcher whose dominance – 617 strikeouts in 582 1/3 innings and a career 3.42 ERA – hasn’t been in question.

Even then, evaluators throughout baseball characterized the Mariners’ return as thin. Sheffield is the prize, and the deal will hinge on his ability to throw strikes as much as it will Paxton’s to avoid the DL. The 22-year-old Sheffield, acquired by New York in the Andrew Miller trade with Cleveland in advance of the 2016 trade deadline, brings an array of frontline stuff similar to Paxton: a fastball that sits around 95 and tops out at 98, a slider he uses liberally and a keep-’em-honest changeup. What he doesn’t do like Paxton is pound the strike zone – Sheffield’s career walk rate in the minor leagues is 3.4 per nine, compared to 9.4 strikeouts – and four evaluators were dubious about his ability to do so well enough to thrive as a starter.

If his control and command don’t grow, Sheffield, two evaluators said, is likelier a back-of-the-bullpen relief type. Considering the quality of the secondary pieces – Swanson, the evaluators said, is a 25-year-old whose peak is as a fifth starter, and Thompson-Williams is a soon-to-be 24-year-old who should start the season at AA – banking on Sheffield to bring back proper value for Paxton is a leap of faith.

For a team like Seattle, which sources said is rebuilding with 2021 in mind, hitting on trades of key players is imperative. Paxton is the second to go after catcher Mike Zunino, who was traded to Tampa Bay in a deal for outfielder Mallex Smith. Shortstop Jean Segura may be next to go, though he has a full no-trade clause, and reliever Alex Colome is attractive to multiple teams in need of bullpen help. Seattle would love to shed the contracts of Robinson Cano and Kyle Seager, though neither is drawing significant interest, according to a source familiar with the Mariners’ efforts to trade them.

Seattle’s inclination to trade Paxton came because it does not expect to contend within his two years of team control. The Mariners’ two remaining most valuable trade chips – closer Edwin Diaz and outfielder Mitch Haniger – could go, too, though Seattle is loath to deal either because of their four years of control. Seattle is trying to thread a precarious needle and eschew a full rebuild when the strength of the American League West – and the top of the AL period – almost encourages them to do so.

It’s a significant risk for a franchise in flux both on the field and off, with former director of high performance Dr. Lorena Martin accusing GM Jerry Dipoto, manager Scott Servais and farm director Andy McKay of racist and sexist comments. Even as the Mariners vociferously denied the charges, they continue to hang over the organization and muddy its direction.

The Yankees face no such issues. Even with Didi Gregorius out for the beginning of the season because of Tommy John surgery, their lineup, with Aaron Judge, Giancarlo Stanton, Aaron Hicks, Gary Sánchez, Gleyber Torres, Miguel Andújar and Luke Voit, among others, is potent. Adding Paxton to a rotation with Luis Severino, Masahiro Tanaka and CC Sabathia is a proper first step. Whether they’re willing to fork over the goldmine Patrick Corbin seeks on a six-year deal, settle for a lesser free agent or hit the trade market for one more starter – Corey Kluber? Carlos Carrasco? Madison Bumgarner? – is the question.

Whatever they do, the Yankees made it clear Monday that they are not going to watch the rest of the AL – and particularly the Red Sox – get better while they sit around. They’re the New York freaking Yankees. Come at them at your peril.

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