No, not perfectly organized invaders, literally any heierarchal group. Because the locals cannot do anything together without consensus. Defence would bw difficult, counter attacking would be impossible or ineffective because the local group would splinter.

Anarchists always seem to ignore the fact that out of the plethora of governmental forms that have been tested by various human civilisations throughout the millennia, anarchism is not one that has ever survived prolonged contact with other civilisations with a different form of government.