Known and feared for their

Known and feared for their (i) ---------, the Prussians became a force inspiring terror after overcoming internal fighting through Bismark’s cunning leadership.
Artillery
Extravagance
Opulence
Covetousness
Truculence

What is the signal word for which “truculence” should be the answer?

There is no single signal word;
‘feared’, ‘force’, ‘inspiring terror’ and possibly ‘internal fighting’ should provide the clues.

Thank you, Beeesneees.

One more:

What does “inspiring terror” suggest?

People were terrified of the Prussians.