I'm very glad that you framed the question that way.
If you look at the proximate triggers and the catalysts for the 2015 migration crisis into Europe, that was because the carrying capacity, or the coverage capacity, of the humanitarian aid to host states in the Middle East decreased so substantially that people had to make the choice to move. That was the catalyst. It wasn't Angela Merkel saying that the doors were open. The timelines don't bear out that analysis at all. That's the answer, and I can share the numbers with you quite readily.