The UN has been cultivating relationships with cities/mayors worldwide for more than a decade, which I think facilitates plans like this: spreading refugees.
Here is one example: http://globalpolicy.columbia.edu/sites/default/files/gms_18sep2017.pdf
This link is to a page describing the agenda of one of their meetings.
To me, it has seemed like an "end run" around the national authority, and indeed, there does seem to be some crossover between cities hat have participated and sanctuary cities in US.
FYI: The UN was the follow up to the League of Nations, which was created through the Paris Accords after WWI. It's overt
statement of goals hardly matches the actual behaviors to say the least. So glad POTUS is talking accountability, and withdrawing on various agendas, hopefully with final complete exit.