Dangerous to whom? When? In what way?
They were, as a Catholic power, dangerous to Protestant England in the 16/17th centuries because they had a mighty army and fleet, lots of money and armies in the Netherlands, and wanted to invade with their Armada.
They were dangerous for much the same reasons when they earlier took over the Netherlands.
Likewise, towards the indeigenous peoples, when they occupied and colonised South American countries and islands.
Peligroso
"peligroso"
Muy peligroso/a
Dangerous Curves - 1992 The Spanish Connection - 2.3 was released on: USA: 30 September 1992
"Una vida peligrosa"
Dangerous Curves - 1992 The Spanish Connection 2-3 was released on: USA: 30 September 1992
"very dangerous"
el juego mas peligroso
"careful, friend. Very dangerous."
peligroso means 'dangerous' (similar to English 'perilous')
to emphasize a dangerous situation
It was most likely included to emphasize a dangerous situation.