When they are no longer invited and come anyway.

When migrants aren't welcome in a country. And no, you are not the voice of our country. As long as people rent out to migrants and/or hire them, they are welcome.

By that logic the Nazis never invaded anyplace. There were people renting out places and selling stuff to them in every country they, um, "immigrated" to.

Id say when it its on course to see the migrants overtake the host population in the foreseeable future.

Then the US had been invaded for the first 150 years of its existence.

Yes, I think that's common knowledge.

An invasion would involve an armed force.

There are maybe 500 million Europeans, and they are taking in 2,000,000 per year. It's hardly an invasion.

As a matter of fact, the real scandal is all the refugees drowning in the Med.

2,000,000? Germany alone took 2,800,000 last year alone!

Depends on if your newspaper has seen a fall in sales.

When force is involved.

Dictionaries can help you with this kind of thing.