A combination of governments or whatever.
As soon as their is a soapbox to standon (silkroad) the politicians will get involved. Sex trafficking, drugs, weapons. its a politicians wet dream.
One successful exchange on the planet could bring the debt based money monopoly to its knees. If only one government allows it or simply fails to contain it their fiat money will be rejected by the market. The overwhelming evidence of stability and growth will flock investment to that region and the idea will be verified. Governments will also not be able to successfully outlaw all trade with that country simply on the basis of its citizens having the freedom to transact in bitcoin.
If there is not complete co-ordination, everyone from Venezuela to North Korea to Washington to Vienna to Mauritius to the Isle of Man to Chile to Zimbabwe to Somalia there will be no way of "crushing" it with legislation.