Avengers: Endgame/Headscratchers

How did the anti-Thanos army come together so quickly?
It was at most fifteen minutes between the Hulk's snap and "On your left", and possibly closer to ten. And WandaVision showed just how much of a madhouse the return from the Blip was. How did all those disparate forces from all over the world get assembled, informed, equipped, and organized in time to make their dramatic arrival in upstate New York, even with the help of the sorcerers?