help on conquering cities

[Romulux]

evertime i kill all the defenders of an enemy city, my troops destroy the city. how do i just keep the city for myself instead of destroying it? ive looked all over the internet and i cannot find out how to just capture a city

 

[hsy]

The city will be automatically razed if it has no culture and only 1 pop (or something like that).

 

[EvilConqueror]

Wait for the city to grow to 2 population.