Haven't read all the replies past the first few, but figured i'll answer this since it happened to me. Forgive me if its been addressed. So i planted a new city and i got pushed to -1 unhappiness. During the time it took to build a colusseum i lost a few pops. The newly built city also lost its one and only pop. Did the city disappear? Nope... it showed 0 citizens. Opening the city screen confirmed that no people were working any tiles. The city grew back to size 1 from the food the city tile produced. What i'm wondering now is... what if the city with 0 pop lost another pop... would it go -1?