The country experiences force labor regarding weaponry making specifically, swords. The production was controlled by the yonkou "kaidou". Why Wano? Because it is isolated. Shipments were sent to Dressrosa to be advertised in the underworld by Doffy. And since it is force labor, the wano people weren't compensated well and haven't eaten anything which made them weak. Due to slow production, Kaidou provides them "enhancement food" like Hody's to increase the number of production but with weird effects, let's say forgetting? or making them insane?.
Kinemon, Kanjuro and Momo haven't eaten anything due to the effects of the "enhancement food" and sneaked out in Dressrosa while delivering weapons.
That's when they were separated with each other.