Why did job specialization emerge in cities as civilizations developed?

the united states broke it's neutrality was the constant german sinking of trading vessels resulting in the loss of lives, one example would be the lusitania.

two cops walk into the bath room,

cop one: well it looks like it was a

cop two: * grabs toast from the toaster thats in the water* yep *eats it*

cop one: *looks at cop two*

cop two: this wet toast is actually really good, why would he waste this?