For decades, the mighty US dollar has reigned supreme as the world's reserve currency, main unit of account, and leading medium of exchange. The go-to for international transactions, it's safe to say that the greenback has seemed untouchable – until now.

US Treasury Secretary Janet Yellen has warned that countries around the world are moving away from the dollar due to fears over America's huge $34 trillion debt and US-imposed sanctions. Meanwhile, the BRICS nations led by China and Russia are making a concerted effort to knock the dollar off its throne, while cryptocurrencies are slowly chipping away at its dominance. So is the US dollar at risk?

Read on to discover how the dollar took over the world, the threats it now faces, and why a major global push to dedollarise could spell catastrophe for America's economy. 

All dollar amounts in US dollars, unless otherwise stated.