Missing countries

I want to use my website for attracting clients worldwide.
I have no idea what country they are from and that should not concern me.

How can a user select which country his property is in?

Hi,
In the Configuration page, tab General, you can select to use all countries on the world. But the main problem is OS Property doesn't have enough location data (states, cities) of all those countries. But you can enter location data by using Manage States and Manage Cities features at backend of OS Property
Thanks
Dam