What if: National religion~

What do you think would be the massive effect on surrounding nations as well as the nation of 1 faith, if entire nations were purely of one religion.

Q:1
Satanism vs Christianity, on a national level.
What would that be like for the people in and around the nation?

Q:2
Taoism vs Christianity, on a national level.
What would that be like for the people in and around the nation?

Q:3
Atheism vs Wiccan, on a national level.
What would that be like for the people in and around the nation?

Keep in mind that each group would have a firm belief in/understanding of the principals.

I think that if people who reply to this have a good understanding of religions and civilization, they will make some very interesting replies.

[waits for replies!] =)