The sudden collapse of a mighty, wicked empire and its massive achievements is never an accident of history. It is a deliberate decree. All the intense effort poured into building human power ultimately crumbles before the Creator. The disaster and punishment that strike the wicked are a direct result of God's planning and retribution.
There are different perspectives on when this downfall takes place. Some view it as a specific historical event, pointing to the collapse of Nebuchadnezzar and the Babylonian empire at the hands of the Medes and Persians [רד״ק]. Others look to the future, viewing the event as a prophecy for the ultimate redemption. In that era, God's glory will be fully revealed to the world, and all the grand achievements of the nations will be exposed as entirely empty and pointless [אברבנאל].
The immense labor invested by these empires is destined for ruin. The primary approach among commentators is that nations work endlessly to build and fortify their cities, yet all their hard work will ultimately serve as nothing more than fuel for a massive fire of destruction. Others suggest that God's anger itself will strike them like a fire until they can take no more [רש״י]. Alternatively, the exhaustion of the nations comes not from their initial building efforts, but from a desperate, futile attempt to extinguish the flames consuming their cities [מלבי״ם].
Every attempt to stand strong and resist is completely in vain, as human wisdom and strength are powerless against God [מצודת דוד]. All their actions yield absolutely no results [אבן עזרא]. While some view the dual descriptions of burning and emptiness as a simple repetition meant to emphasize the total failure of the empire [רד״ק], others draw a deep distinction between the groups experiencing the downfall. According to this perspective, the general masses physically exhaust themselves with manual labor, desperately trying to save their burning cities. In contrast, the distinct nations bound by religion and faith quickly recognize that the destruction is orchestrated directly by God. This sudden clarity paralyzes them with internal weakness and despair, as they understand from the start that any attempt to fight back is utterly useless [מלבי״ם].