"When you buy enough stocks to give you control of a target company, that's called mergers and acquisitions or corporate raiding. Hedge funds have been doing this, as well as corporate financial managers. With borrowed money you can take over or raid a foreign company too. So, you're having a monopolistic consolidation process that's pushed up the market, because in order to buy a company or arrange a merger, you have to offer more than the going stock-market price. You have to convince existing holders of a stock to sell out to you by paying them more than they'd otherwise get."