Countries can banned BTC/Cryptocurrency but they can't stop it. I believe there are still lot of people doing business in cryptocurrency even though the government banned those things.
Bitcoin is ban in many country due to some reason. Bitcoin ban in china, Ecuador, North Korea, Bangladesh, Israel etc. At first Bitcoin ban in china. And at that time it makes big impact on Bitcoin price. China government ban it because it directly affect their own currency which ultimately affect their country economic growth value so their politicians put pressure on government to ban it. Ecuador, North Korea like country also because bitcoin put negative effect on their economy because it s user doesn't pay tax to their government. In country like Israel it is ban because bitcoin associated with many criminal activities. 