In Luke's version of Jesus' Jerusalem discourse, the warning becomes unmistakably military: when Jerusalem is surrounded by armies, its desolation is near. Those in Judea are told to flee rather than seek security inside the city.
The instructions reverse the normal instinct to take refuge behind fortified walls.
Ancient populations often fled to fortified cities during invasion, but once a siege closed around a city escape could become impossible. Defeat could bring killing, enslavement, forced displacement, and the humiliation of conquered territory.
Jerusalem experienced precisely such catastrophe in the Jewish revolt against Rome, culminating in its capture in AD 70. Luke's language of captivity and the city being trampled by Gentiles belongs naturally to the political realities of conquest.
The historical setting gives urgency to Jesus' command to flee. The city that normally represented security would itself become the center of danger.
It also explains the severity of the prophecy: destruction is not limited to damaged architecture. War scatters people, transfers political control, and subjects a sacred city to foreign power.