How could the Nazgul take Minas Morgul?

[Tuor in Gondolin]

Originally Posted by FeRaL sHaDoW
I think i have read somewhere that the Nazgul have some power to influence or take control of people. Couldent they just turn the city people agaisnt them selves. Then in the end wouldent the nazguls just have to walk in.

Good point. Whatever mechanics were employed outside, an equally important process of demoralisation, corruption and treachery was doubtlessly occurring within. We need only to look at Sauruman, Denethor and Theoden to see how good men, in Tolkein’s world, are almost imperceptibly brought down.
No doubt the end was ushered in by some small gate opened by the hands of a traitor in the dead of night, some poor orders from the captains and downright self-serving foolery or cowardice by others.
Would it not be in character to speculate that the place was as much ‘lost’ by those entrusted with its defence as it was ‘taken’ by those who wanted it?

What I like about this suggestion is that it gives a
reasonable explanation of how the palantir was captured. If
the fortress was captured by stealth then the palantir would have been
valuable as a communication device with Minas Tirith for the
Gondorians who, presumably, did not think that their fortress
was in iminent danger of being lost.