Current state of regulation of Bitcoin

I was wondering about how Bitcoin sites are being regulated at this point in time, in several different locations including the United States, the United Kingdom, Canada, and the European Union.

For example, if I were to start a cryptocurrency exchange in the USA, what regulations am I subject to? I know that there are KYC and AML regulations, but are these only applicable when there is fiat USD involved?

Also, if such an exchange were to operate in multiple countries, such as the United States and Canada, would US regulations only apply to US residents, and Canadian regulations only apply to Canadian residents?

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