Which city is considered the capital city of country?

The main thing that makes a city the capital city of a country is that the government has its base there. The representatives of the people or whoever is running the country work there. Other elements of government are based there, like headquarters of departments or government organisations. A lot of other organisations and companies will have their bases there. Usually a capital city is the largest city in a country, though not always. If it is not the largest, it will be one of the largest.