The collapse might happen in waves, many waves. Some financial, others social, and God, hope not even war/severe social unrest.
It is also not likely to affect all parts of the world. Some areas will be devastated.
I don't see the collapse as something from a "single piece". It will be like a puzzle, but many pieces will be nightmare scenarios.
Massive migration could ignite. What's odd is the flux of migrants since around 2015 towards prosperous countries: the US, the EU. Some did actually predict mass migration, but as a "possible scenario" sometime far in the future (as a result of depleted natural resources, arid lands, wars and social unrest).
Africa is moving to Western Europe.
Guatemala and El Salvador to the US.
New dark ages?