Question

Why does a country need a capital at all?

Answer 1

Country need a capital for Ease of Governance.

It just makes sense to have all the wings of government together in one place. Separating them out to different cities for whatever reason would only make things harder, both for the government and for the people. 

Answer 2

A country may have a great diversity in culture, language or religion which may not be very easy to handle or administer. thus a country has a capital from where it can administrate the whole country's affairs. This makes the administration and control of all diversities easy and prevents conflicts.