Why is it not possible to access some websites from some countries?

Question

For instance i could not access action forex website again from nigeria

Answer 1

Could be anything from limitations imposed by your country, routing glitches, or the website not trusting certain locations.

Nigerian scams were famous long before the internet (my boss received them via air mail) and the internet has widely expanded that.  So if people have sent such spam from your ISP, it might be blocked, and you end up suffering for what someone else did.