Baghouz, Syria -- It still wasn't completely clear Thursday morning whether ISIS had been definitively defeated in the terror group's last tiny sliver of territory in Syria, but CBS News correspondent Charlie D'Agata said that what had for months been a vicious battle, appeared all but over.

At its peak in 2015, ISIS held an area across Syria and neighboring Iraq almost the size of Indiana. But four years later, they held less than a square mile at the beginning of this week, and the final battle was on to recapture the patch of ground in Baghouz, eastern Syria.

For two months, D'Agata has been with the U.S.-backed fighters leading that battle against ISIS. He said on Thursday that there was still some fighting to be done -- the ISIS camp needed to be fully searched before America's allies would declare outright victory -- but from he saw, that victory certainly looked close.

As a member of the U.S.-backed Syrian Democratic Forces (SDF) sat on the ground fiddling with a blade of grass, D'Agata said he'd never seen the battle-hardened forces on the frontline of the fight against ISIS looking so laid back.

One look at their faces was enough to know the final fight to completely deprive ISIS of territory had just about come to an end.

After weeks of airstrikes, heavy bombardment and close quarters fighting, D'Agata said it was tempting on Thursday to describe the scene as almost peaceful.

Without the backup of 2,000 American troops on the ground, and tens of thousands of U.S. and coalition bombs from the air, victory would have been impossible.

But the bulk of the fighting came down to the Syrian Democratic Forces.

Asked what the end of the grueling battle meant to him, SDF officer Chiagar Amad told D'Agata that he was filled with "a mix of great happiness and sadness. Many of our comrades have been killed in this fight."

The SDF has done the lion's share of the on-the-ground fighting against ISIS in northern and eastern Syria, and with scant supplies. D'Agata watched as the forces spread mud across their vehicles as makeshift camoflage. But he said that what they lacked in equipment, they more than made up for with courage.

The defeat of ISIS on the ground is a major milestone, but D'Agata said that tens of thousands of ISIS fighters have melted away, and will continue to threaten the security of the region.

D'Agata reported in January that the terror group was already shifting tactics, launching attacks in regions far from their previous strongholds as they lost their footing. The group's metamorphosis from ruthless rulers of a self-declared "caliphate" into an insurgency has already begun.