Here's a short answer. For over 100 years the US has been operating on the assumption that money pumped into the top levels of the economy will eventually trickle down to the masses, i.e. money spent on huge, capital intensive projects will create jobs and use materials that will themselves create jobs, etc.
But in practice, it doesn't work that way. In practice, money acts more like cream - it rises to the top and stays there. That's why there is such a small percentage of the populace that are super rich, while most of the population is getting poorer and we're losing our middle class. Records show that small businesses are the ones that provide the greatest employment, but that's not where the money is now and small business are going bankrupt right and left.
Connected to that practice is the concept of scarcity, promoted by charging interest on loans. Paying interest means you are paying more than you borrowed. Where does the extra come from? In repaying loans you, and everyone else who borrows, become a sort of money scoop that sends yours and others' money back to the banks. In other words, the banks scoop up all the "extra" money out there, through you, by charging interest, thereby keeping control of the economy.
In the Middle East the Q'uran forbids the charging of interest (usury). The US has been trying to force it on them. That's one of the many reasons we have war there. It isn't just about Israel or nuclear power.