A surge in the dollar has benefited many Americans and reinforced the country's economic strength — but it has also caused a lot of pain for others.

The dollar has helped make the U.S. the most economically powerful country for most of the last century, but other countries — including rivals like China — have the greenback on their sights.

Customarily, the Fed and other central banks do as much as they can to keep markets calm. This time they're the reason behind the volatility.