Absent of any other context one might reasonably assume "1990" Refers to 1900 CE. But we have additional context, such as:

"Cities had guards.", "you were mostly at the whims of thieves and pirates."

What in that speaks to 1900 CE over 1900 BCE? There is evidence of pirates in both time periods, so that feature alone isn't telling. But the context doesn't end with that feature in a vacuum, does it?