Midfielder Perry Kitchen of D.C. United dribbles the ball against Philadelphia last week. United won, 1-0. (Hunter Martin/GETTY IMAGES)

Rivalries are ingrained in soccer’s soul, ancient conflicts defined by geography, class and religion. They’ve furnished the Buenos Aires derby between Boca Juniors and River Plate, Spain’s superclasico matching FC Barcelona and Real Madrid, and Glasgow’s sectarian standoff with Celtic and Rangers.

Founded in 1996, MLS has neither the history nor roots for deep-seated enmity between clubs or global awareness. But the league’s growth has cultivated young rivalries of varying intensity.

On Sunday, simmering animosity will surface on both coasts. After recent expansion entrees from Portland and Seattle collide in the league’s fastest-developing clash, D.C. United will meet the New York Red Bulls for the 68th time in all competitions.

This D.C.-New York affair has the making of a traditional scrap overseas: Red Bull Arena, a European-style venue within walking distance of a commuter train stop, is sold out (25,000). United shunned usual air travel and hopped aboard Acela on Saturday for the trip north.

A week after 500 United supporters invaded the Philadelphia Union’s PPL Park, an estimated 250 are traveling to Harrison, N.J. The match falls three days before the first anniversary of United’s blockbuster trade with New York: 2011 league MVP Dwayne De Rosario for industrious midfielder Dax McCarty.

Three points separate the clubs in the upper tier of the Eastern Conference — the difference coming from United’s 4-1 victory in the first encounter in April at RFK Stadium. The Red Bulls will visit Washington again in late August.

“Rivalries bring massive energy, attention, support, atmosphere — and usually they have some meaning to them,” D.C. forward Josh Wolff said. “It has importance for the players and the fans. It doesn’t take much to get you motivated.”

MLS put greater emphasis on rivalries this year, breaking from the global standard of home-and-away games between all 19 clubs. Instead, most teams will face in-conference foes three times apiece and non-conference opponents once.

While many decried the decision, United Coach Ben Olsen was among those supporting it.

“We are, in a lot of ways, a unique league,” said Olsen, who, as a player, assistant coach and head coach, has prepared for New York every year since 1998. “I look at it from a player’s point of view: I liked to play in games that meant a little bit more. I appreciate the history and have fond memories.”

Olsen also cited fans’ ability to attend additional conference games, which lightens the expense and time commitment compared to trips to, among other places, Seattle and San Jose.

Small countries don’t have such issues. In England, the 20-team Premier League will feature six London-based clubs next season.

Stoking rivalries wasn’t MLS’s only motivation; it also wanted to reduce travel demands in a league spanning a continent.

Like in college football, rivalry trophies are at stake. United and New York play for the Atlantic Cup. Seattle, Portland and Vancouver vie for the Cascadia Cup. Dallas and Houston want El Capitan, a 19th-century cannon.

Toronto and Columbus tussle over the Trillium Cup, named for a flower found in both Ontario and Ohio. Real Salt Lake and the Colorado Rapids pursue the Rocky Mountain Cup. FC Dallas and the Chicago Fire are after the Brimstone Cup, a name forged when the Texas team was known as the Burn.

The most natural rivalry features the Los Angeles Galaxy and Chivas USA, roommates at Home Depot Center.

A native of Argentina, United defender Emiliano Dudar has experienced soccer’s regional strife. Aside from Boca Juniors vs. River Plate, the country offers numerous local and regional rivalries.

“You live the whole week with anxiety and higher adrenaline than for a normal game,” he said through an interpreter. “You notice it in every player. I was filled with happiness because they are special matches. As a player, you are thankful for these chances.”

United notes: Defender Ethan White was loaned to the third-division Richmond Kickers for two matches. He also had appeared in two other recent Kickers games. . . . United’s injury list, once a source of major anxiety, is down to one player: rookie midfielder Lance Rozeboom (knee surgery). . . . Red Bulls winger Dane Richards is serving a one-game suspension for yellow card accumulation.