Final answer:
The correct word to fill in the blank is 'invasive,' as it fits the context of the passage which involves armies threatening to attack and hinder the nation's defense efforts.
Step-by-step explanation:
The passage describes a time of great uncertainty and distress, where threats seemed imminent, and the nation's ability to mount a defense was hampered by internal challenges. The correct word to fill in the blank describing the armies would be 'invasive,' as it suggests that these armies are entering and attacking the nation, just as the passage indicates the nation’s defenses are being obstructed. Words like 'subnormal,' 'informative,' and 'hesitant' do not fit the context of threatening armies.