It had been held by the Russian army for more than 6 months.

But by September 8, the Ukrainian army had recaptured it.

And they were just getting started.

Over the next few days, Ukrainian forces swept through this Russian-held territory

with astounding speed.

"Ukrainian forces have blitzed through Russia's gains..."

"...in a lightning counter-offensive..."

"...forcing Russian forces to retreat..."

As of September 14, Ukraine claims it recaptured

nearly 8,000 square kilometers of Russian-held territory

and liberated dozens of towns.

It's a major breakthrough for Ukraine and it marks a new phase in the war.

So, how did Ukraine pull off such a stunning attack?

And how does it change the war?

It's useful to think of the war in Ukraine as having three main phases, so far.

The first began when Russia invaded in February 2022.

The Russian military swept into Ukraine through the north, east, and south

and immediately clashed with the Ukrainian army.

This phase was essentially the Russians attempting to force

the Ukrainian government to surrender.

This is Mason Clark, a Russia analyst

at the Institute for the Study of War, an American think tank.

Ukrainian forces at the time were in large part outgunned.

The most intense fighting took place in a few major cities

like Kharkiv, Mariupol, Kherson, and outside the capital, Kyiv.

But by April, a few weeks into the war

Russia had failed to capture Kyiv or Kharkiv.

It did control a large swath of territory, though

and continued to fight the Ukrainian army on three main fronts:

In the northeast, in the east, and in the south, where it did control Kherson.

That's when the second phase began.

From about April to August, this map changed very little.

Russia, for the most part, stopped conducting large, sweeping attacks

and instead relied on its artillery to pound Ukrainian positions.

But the Russian army was in bad shape.

The US government estimates that as many as 80,000 Russian soldiers

have been killed or wounded.

It was very, very devastating for them

particularly since the losses they were taking early in the war

were in the the best of the Russian military.

The easy comparison is

by this summer, the Russians had lost more men than the Soviets did

in nearly a decade of the war in Afghanistan.

So, during the summer, Russia used the time to recruit more soldiers.

But it didn't go well.

A fascinating element of this is that

the Kremlin still is calling this a special military operation.

It cannot be referred to as a war.

That actually matters because the Russians haven't called up conscripts for this invasion.

And instead, they're trying to fill these gaps with these various ad hoc methods.

The Russians have had to hire more mercenaries.

And offer payments to prisoners.

They've even raised the age limit to allow men over 40 to join the army.

And Russia's sent many of these men, with little training, to the front lines.

So it's led to a steady drop off in the quality of Russian personnel throughout the war.

But while Russia struggled to rebuild its army, Ukraine had the opposite problem.

There was actually a sort of bottleneck in May

where they had too many recruits and not enough instructors to train them

which is a very good problem to have.

With help from its western allies

Ukraine was able to quickly train lots of these men

before sending them to the front.

That has really helped the Ukrainian military not just produce more soldiers

but very effective soldiers, better than the Russians.

By the end of August they were ready for the next phase of the war.

Their own attack.

Throughout the summer, Ukrainian leaders talked a lot

about their plans to launch an attack.

And they made it pretty clear that they would strike here, Kherson, key to control the south.

Ukraine moved many of its troops into position near the city.

And used their most-advanced artillery to hit the Russians for weeks.

They were forcing the under-manned Russian army to make a choice:

they had to pick somewhere to send forces and they picked Kherson.

When the Russians moved troops to Kherson, they left the northeast vulnerable

since it was mostly guarded by those experienced soldiers.

So when Ukraine did start their attack in early September

they didn't hit much resistance there.

Almost as soon as Ukraine's soldiers began the attack, the Russian forces began to flee.

These are piles of weapons and ammunition, left behind by Russian troops near Kharkiv.

They also left trucks, tanks, and artillery behind.

And this is a Russian tank crew frantically fleeing

before crashing into a tree.

The Russians were running away and withdrawing

faster than the Ukrainians were keeping up with them.

While the Russians retreated

Ukraine took over all this territory

which included some important towns.

Izyum was a Russian supply dump.

And Kupiansk was a crucial railway hub, useful for moving troops and supplies.

They've also freed thousands of Ukrainian civilians

that have been trapped under Russian occupation for months.

I think this was a very well done, opportunistic attack

that went just incredibly well for the Ukrainian military.

Meanwhile, Ukraine is still attacking Kherson and making some progress.

But the attack in Kharkiv has begun a third phase in the war

where Ukraine, this time, has the momentum.

There's a long road ahead.

The Russians are going to try and replace these further catastrophic losses

with likely diminishing returns.

But I am confident in saying that the shoe is more on the other foot now

with Ukrainian forces having the initiative of choosing where

the next major battle of the war will occur.

And they have clearly demonstrated

that they can and fully intend to take this war into 2023

and drive out the occupying Russian forces.