They ain't declaring the war. They cannot control the cryptocurrencies and that is their main problem. Instead of the war for prevailing, they had already chosen the way to adapt and that is making some usage of the cryptocurrencies to give them more benefits.
A tax system is happily embraced by the government when the crypto is included. Taxes from the crypto means additional income for the country.
They were fighting at the beginning but the smart countries are now seeing the possible benefits of adapting to the crypto market.