>>Due to a massive growth of money offered for such special treatment by foreigners or due to fast integration of foreigners into places where they could act on their imported corruptedness?
The latter. But actually some corruption is so entrenched that it's regarded as business as usual and goes under the radar.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1