What's the difference between a VMCA departure and a spin entry?
For a spin, we increase AoA to the stall, and induce a yaw input using rudder (deliberate, or unintended through mishandling of the rudder), the inner wing lets go and drops, followed by the nose, and you're spinning. I know this having done it deliberately literally hundreds of times.
I'm not a multi-engine pilot so VMCA is theory to me. However, as I understand it the mechanism is similar to that of spin entry, except the yaw is induced by assymetric power overcoming the ability of the rudder to compensate, due low airspeed. Also, a VMCA departure can presumably happen when both wings are (before the event) below stall AoA. But the outcome is the same - inner wing stalled, un-commanded wing drop, and you're spinning.