In most cases, shaded areas, like this red

are meant to symbolize territory occupied by Russian forces

or at least, territory Russia and Ukraine are fighting over.

In general, this red is referring to ground troops, like these.

The more the Russian ground troops advance, the more of the map turns red.

But what maps like these don't show is another battle

that's taking place high above Ukraine.

Where a small Ukrainian air force is fighting a powerful Russian one

for control of the skies.

What happens here could determine not just the course of the war

but whether it escalates and spreads beyond Ukraine.

It's why Ukraine's allies are scrambling to send it weapons.

And some are asking to go a step further:

"No-fly zone."

"No-fly zone."

"A no-fly zone."

[chanting] "No-fly zone!"

"A humanitarian no-fly zone."

"No-fly zone seems to make sense."

"Well, I think you that all know what I'm going to say."

"We need the no-fly zone over Ukraine."

So, why are the stakes of this air war so high?

And what would a no-fly zone change?

On February 24, 2022, the Russian invasion of Ukraine began.

And in terms of military strategy, it followed a common script.

First, Russian missiles targeted Ukraine's radar system.

Then its airfields and some missile launchers.

To military experts, this appeared to be preparation for a crucial step.

Send a lot of planes to destroy the Ukrainian air force

and achieve what's called “Air Superiority."

So when we say a military has air superiority

what we're essentially saying is a military more or less controls the skies.

With air superiority, Russia could freely attack Ukrainian ground troops

and protect its own ground troops

who could move faster without fear of being attacked from the skies.

If Russia were able to establish virtually unchallenged air superiority

it would be a disaster for Ukraine.

Doesn't mean you're guaranteed a victory

but it makes that victory a heck of a lot more likely.

That's why since World War II

winning air superiority has been the first step in most invasions.

But in this case, the big attack never came.

And experts don't really agree on why.

My best informed guess is that

Russians thought that they would be welcome when they got there.

And so when they saw men, women, and children

blocking their tanks from entering Ukrainian villages

that surprised them.

When you make war plans, including plans related to air superiority

if your assumptions are wrong, then your plan is messed up.

Whatever happened, it means that, more than two weeks into the invasion

Russia did not have total air superiority.

It allowed the Ukrainian air force to defend themselves

against some Russian fighter jets and ground forces

helping bog down the Russian invasion.

This was celebrated as part of Ukraine's remarkable resistance early on in the war.

It's a function of both Ukrainian success and also some surprising

shortcomings in Russian military capability.

But it might not last much longer.

When you compare the Russian military and the Ukrainian military there is no comparison.

In every major metric of power, the Russian military is far more powerful

including when it comes to aviation.

Russia has more than ten times the number of fighter aircraft as Ukraine.

And so far, they haven't really used them.

It's possible over the coming days and weeks that Putin and his military leaders decide

to make greater use of Russian aircraft.

And I think that's already happening.

They're entering a new phase where, in my view, they're systematically

using air power in part

to systematically attack civilians and civilian infrastructure.

That means the Russians still could win air superiority

which would help speed up their invasion, and likely cause significant civilian casualties.

So, Ukraine's allies are frantically trying to keep that from happening.

Many countries are sending weapons

that Ukrainian ground troops can use to shoot down Russian aircraft.

And there have been talks about sending Ukraine planes.

But there's also been talk of another kind of help: a no-fly zone.

Ukrainian president Volodmyrr Zelenskyy has asked NATO, the western military alliance,

to declare a no-fly zone.

A number of US foreign policy experts have called for a limited no-fly zone

and a recent poll shows 74% of Americans think the US should declare one.

So, what is a No-Fly Zone?

Basically it's a geographic area, where certain plains are prohibited from flying.

The point of NATO declaring a No-Fly Zone over Ukraine

would be to prevent Russia from winning air superiority

thereby protecting Ukraine's military and civilians.

But what makes a no-fly zone complicated is how NATO would have to enforce it.

To propose the no-fly zone in Ukraine

if you're going to be serious about it, you have to consider that to enforce it

to make it a real thing

you would actually have to shoot down Russian aircraft.

This means NATO would be directly participating in the conflict

escalating the war to involve the US and most of Europe.

The establishment of a no-fly zone sooner or later

puts us in a high risk of direct combat.

And don't for a minute think that you can control how that escalates.

Once one aircraft gets shot down, whether it's ours or theirs

all bets are off on what happens next.

Russia is a nuclear armed power and Putin's been making a lot of threats to suggest that

he thinks nuclear weapons might be an option.

All this would also be true of a "limited no-fly zone"

which would only cover certain areas, but would be enforced in the same way.

Putin has vowed to treat anyone imposing a no-fly zone as a “participant in the conflict”.

And, so far, president Biden and NATO leaders have ruled it out.

So for now, even while its allies send weapons

Ukraine will have to do the fighting themselves.

Every bone in my body wants to help Ukrainians.

They're fighting for all of us, and I weep when I see some of these images.

But I think we should do all that we can to help Ukraine

while also doing everything we can to avoid direct conflict with Russia.