An invading army, taking possession of conquered territory, could not have looked more confident than the New York Mets as they congregated on the infield here at Wrigley Field to celebrate their four-game sweep of the Chicago Cubs to win the National League Championship Series on Wednesday night. But that’s how a mass of Mets troops should feel when they know that their generals are four young power pitchers now making a place in history: Matt Harvey, Noah Syndergaard, Jacob deGrom and Steven Matz.

Each started a game against the Chicago Cubs, in just that order. Their combined ERA: 2.16, plus three wins and, for the 22-year-old Matz in Game 4, 42/3 innings of classy work. The final scores tell the crushing truth of what a thunderous, poised, dominant rotation does to superb young sluggers: 4-2, 4-1, 5-2 and, to wrap up this series, one final almost casually easy 8-3 victory to ensure a trip to the World Series next week.

“I’ve been a huge baseball fan since I was 4 or 5 years old,” Mets Manager Terry Collins said. “My mom wrote me a note to skip school so I could watch the Pirates and Yankees in the World Series [in 1960]. Now you’re going to be in it after all these years.”

So blunt was this 21-8 total-score Cubs whipping, on top of a five-game playoff win over the Los Angeles Dodgers, who had home-field advantage and a pair of superstar hurlers in Clayton Kershaw and Zack Greinke, that the Mets might as well have held up index fingers, as in “That’s one.”

The New York Mets celebrate after completing a sweep of the Chicago Cubs in Game 4 of the NLCS. (Nam Y. Huh/Associated Press)

Mets second baseman Daniel Murphy, he of the same name as “Murphy the Billy Goat” in the famous Cubs Curse, naturally had another home run (and four hits), giving him homers in six straight postseason games, the first player to manage the feat.

The Mets’ victory in this series — and the sudden, unexpected arrival of a truly gifted Cubs team — made this NLCS feel like the start of something fresh and fun. All others in the NL, take notice.

The young Cubs returned to the field 10 minutes after their loss to long cheers. Their future looks like it should be wrapped in rainbows. Take a good look at them as they exit the 2015 stage because they’re about to become recurring nightmares — with all these players under team control through 2020: rookies Kris Bryant, Kyle Schwarber, Addison Russell and Javier Baez as well as Jorge Soler, slick infielder Starlin Castro and cleanup bomber Anthony Rizzo.

Memorize that list. Then you barely will have to look at the scoreboard to fill out the Cubs side of your scorecard when Chicago comes to your town.

Three months ago, the NL looked the same as it had in recent years. The traditional baseball blue-bloods with the recent World Series rings were in St. Louis and San Francisco. The mega-money team with a $310 million payroll was in Los Angeles. The talent, if you listened to the Nationals as well as 100 prognosticators, was in Washington. And if you wanted pluck, you had the Pirates.

The revolution on display in this NLCS was not simply hidden by the mists of the future. If, as late as the final days of July, you had said that the Mets and Cubs would play for this season’s pennant, you might have gotten odd looks, even in Queens and here on the North Side.

The future for both franchises: sunny and bright. The present: partly cloudy, with a chance of catching lightning. But who knew what would happen — and so fast?

On July 28, the Cubs were a pleasant 52-47 but 111/2 games out of first place. On July 30, the Mets were 52-50, three games out of first place and uncertain whether to buy or sell at the trade deadline.

Then the entire picture of the NL changed, probably for the next several years.

The Cubs took off first, going 15-1, at roughly the same time that the 6-foot, 230-pound Schwarber, called Hulk the Schwarb, became a lineup fixture. Hitting in front of Bryant (26 homers) and Rizzo (31), Schwarber hit 16 homers in just 232 at-bats and completed a perfect left-right-left trio.

“A year ago at this time, he was in the instructional league,” Cubs Manager Joe Maddon marveled. Schwarber, the No. 4 overall pick in the 2014 draft, spent fewer than 150 games in the minors.

The Cubs woke up first, but the Mets woke up best. Just before the July 31 trade deadline, they pulled the trigger to acquire slugger Yoenis Cespedes. They also dealt for setup man Tyler Clippard. Suddenly, a team that was averaging fewer than three runs per game the previous month led the league in scoring after the all-star break.

The Mets left a vapor trail as they went 31-11 to obliterate the Nationals, pushing them 9 1 /2 games behind and leaving Washington so discombobulated it has fired everybody except Teddy — and he’s under review.

Baseball is now the “sport of parity,” perhaps more than the NFL has ever been. Of the four baseball finalists, not one is in the top nine payroll teams in MLB. Their average rank is 15th.

The Dodgers have proved that money isn’t enough. The Nats have shown that talent isn’t sufficient alone. The Cardinals and Giants have shown the perennial power of brains and proper player development. With a spacious park, the Mets went for power pitching in such quantity that few have even noticed the absence of fireballing Zack Wheeler, who missed the season recovering from elbow surgery. The Cubs built a lineup designed to make Wrigley the Unfriendly Confines for visitors for many years.

Pick a style and win a while. The NL could be a mad house every year with postseasons just as unpredictable as 2015 when every round, including the wild-card game, was won by the team with fewer regular season wins. Or, if you’re mean, the fifth-best team won the pennant.

If the Dodgers, Cardinals, Giants, Nationals and Pirates think that they can change their fate in 2016 by hiring a new manager or fixing one or two obvious faults, that’s probably a delusion. The NL has been dominated in interleague play for years. But such breadth of talent may change that.

“I oftentimes look out on the field, and I look at short, third and left field, and I’ll see KB [Bryant], Addison and Schwarber and think, ‘Wow,’ ” Maddon said before Game 4. “To have gotten to this point already — this is just the beginning. . . . This is all based on scouting and development. I get to walk in the door and find all these riches inside.”

The Mets love their prospects, too, but with an asterisk they don’t try to deny. They “went for it” this season and have driven their superstar starters harder, through far more innings and high-pressure games than they have ever faced. And at young ages. Harvey, like Wheeler, already has had one Tommy John surgery. What price, pennants? The Mets are willing to pay that freight, though they don’t know yet what it is.

“We think we did the right thing. . . . Everybody is allowed to have their own say,” Collins said of Harvey, who is over 200 innings despite zero innings last season, and Syndergaard, 23, who is far beyond his minor league totals and still has a World Series to pitch.

“When it’s all said and done, we don’t know what’s going to happen next year and how they’re going to feel coming out of it,” Collins said. “But I’m looking at guys here in October, which none of them have ever performed in, still throwing the ball 98. . . . Now we’ve just got to go play it out. I’m not looking for vindication. I believed in our system.

“We had some controversy along the way, but it comes with the territory.”

And where is that Mets territory? After this night in Chicago, the Mets hold sole ownership of all National League rights to play in the World Series.

In New York, where the Mets haven’t held such a party in 15 years, that NL flag, plus hopes of a World Series title, will go a very long way toward answering all questions.