Hillary and Obama did this when they allowed Libya to be plunged into chaos.
The only way to stem this is to deliberately sink the boats bringing them over. Send a few of them to the bottom of the Mediterranean and migrants may weigh other options.
That would work for the newcomers, but what to do with the ones already entrenched? The Italian government seems to be siding with the EU edicts, and will put the interests of the invaders above those of their own citizens.
It’ll be a chore to round them all up and ship them all back, but that’s the only way to clean up that mess. In the mean time, Italians are going to be assaulted continuously while their government sits on their hands.