Actually, taxation plays a large role in giving a currency value. The US government only accepts payment in US dollars. They require everyone to pay taxes in US

Actually, taxation plays a large role in giving a currency value. The US government only accepts payment in US dollars. They require everyone to pay taxes in US dollars, which means we all seek US dollars. Add onto that the fact that the government has and uses tools to control inflation and deflation means we have a relatively stable currency. We know that the US government's long term intention is its continuity. (We do not know the intention of the Chinese mining pools that control large portions of Bitcoin, though, we can assume profit and not stability.) Tie all that into one of the strongest economies in the world and you have yourself a reserve currency.