By attacking Russia’s Kursk region, Ukraine took advantage of the window of opportunity that’s opened as the United States focuses on its presidential election. And it changed the course of the war.

The raid came as a complete surprise both to Russia and to Western allies overly concerned with enforcing dictator Vladimir Putin’s “red lines” and the specter of escalation.

The offensive has been a stunning success, and it quickly won the approval of Western allies and the public.

The situation on the ground, too, was ideal for such an operation: Ukraine was able to amass enough troops in the Sumy and Kharkov area under the guise of needing to protect that region from a potential Russian invasion without arousing Moscow’s suspicions.

At the same time, Russia threw all its resources into offensive operations in the Donetsk and Zaporizhzhya areas.

Moreover, Ukraine conducted a successful disinformation operation to mislead the enemy, focusing attention on a possible Russian offensive from the north. That further helped put the Kremlin to sleep.

The raid had been in preparation for months. And clearly it was planned perfectly.

Ukrainian troops faced an almost empty Russian rear, which Moscow was unable to protect.

Most important, though, Ukraine changed the very nature of the war: Its forces were able to move away from the Russian-imposed, resource-based, World War I-style trench warfare, with its creeping offensives paid for with thousands of soldiers’ lives.

Instead, it triggered a “mobile war” for which the Russians were unprepared.

The result will give Ukraine the big advantage. Russia does not have sufficient resources to defend its vast territory.

The raid also revealed several things Putin will find unpleasant.

First, it turned out that there were no “red lines” the West was afraid to cross to avoid angering Putin. The West had grossly overestimated the Kremlin’s threats.

Dmitry Medvedev, the deputy head of the Russian Security Council, for example, didn’t write a single post on social networks vowing to turn the “Anglo-Saxons” into radioactive ashes.

And Ukraine wound up contributing to NATO’s security: Russia has begun to withdraw troops from its western borders, including in Belarus and Kaliningrad.

The raid also showed Russians themselves weren’t ready to defend “native Russian lands”; they fled the theater of war en masse.

Those who remained did not offer any resistance and surrendered.

Something similar happened during last year’s revolt by the head of the Wagner Group, Yevgeny Prigozhin, who without a single shot captured the million-strong city of Rostov, where he was welcomed as the leader of the nation.

Nor are Russian elites in any mood to fight. During that revolt, of the 89 heads of the Russian Federation’s constituent entities, only 10 went public with their support for Moscow’s power. The rest waited to see who’d get the upper hand.

Fact is, Russia is weak. During 2½ years of war, all it’s got to show for its efforts is an impressive group of troops amassed in a fairly small area of eastern and southern Ukraine, won at the cost of the lives of countless soldiers — who, notably, are already in short supply.

And Putin won’t announce another mobilization: The last time he announced one, in 2022, Russians fled abroad en masse and burned recruitment offices.

The “Russian Empire” is cracking.

Prigozhin’s rebellion showed that with 5,000 fighters, it’s possible to reach Moscow without resistance.

The Kursk raid exposed the holes in Russia’s border and that its territories have no one to defend them.

Soon the Kursk operation will be expanded further into enemy territory, including as far as the M-4 highway, which leads straight to Moscow.

We’ll see strikes on Russian logistics and communications operations that serve Russia’s Donetsk front.

Certainly, all talk of Ukraine surrendering and making territorial concessions is now off the table.

History is full of examples of how empires crumbled at the hands of a seemingly weaker opponent.

Only one question remains: Are you with us or not?

It’s a question for the next US president.

America could share in Ukraine’s triumph by providing it with the weapons it actually needs and allowing it to use them while destroying Russia’s military infrastructure.

As Republican Sen. Lindsey Graham said after the Kursk raid, “Putin started it. Kick his ass!”

The only choice now is: Do you want Russia to win — or Ukraine?

Oleg Dunda is a member of the Ukrainian Parliament.