The Federal Reserve
The Fed is a private bank that runs America. Likewise the Bank of England in the UK. Let's say that again - a private bank owned by private individuals which is beyond the power of the President or Congress ... and it can do whatever it likes, and it does. It has operated like this since President Wilson opened it in 1913. He later regretted this.
To understand the system we have: The Money Masters (Part 1 - follow the links for the rest)
Central banks have come and gone in American history eight times and there are now moves to abolish it again, fronted by Ron Paul. For more information check out his Campaign for Liberty website.