It could be both , depending on the meaning the sentence is trying to convey
"Justly" is an adverb and means in a just manner .
If the sentence wants to refer to the fact that the bankruptcies are justified and happened fairly according to certain previous flaws or other economic deficits ,then 'Justly' could be used.
"Just" is both an adjective and an adverb .
Here it would be an adverb and means "exactly ".
It could be used to indicate ,that what happened in the 20's is exactly the same like what occurred in the 80's .
One is more likely to use 'just' in this context , I think ! Yet if you read this sentence in a document ,then they mean it in the first sense !