It has been a tumultuous week for the stock market, as Donald Trump’s quest to reshape the global capitalist order has sent investors into a frenzy. Where is all of this headed? Who knows. But going into a possible trade war, it’s worth stepping back to reflect upon the shape of our financial system.

To start: What are the most important developments on Wall Street in recent years? The short answer: massive asset managers — above all, the “Big Three” of BlackRock, Vanguard, and State Street — have become the dominant players in the financial system and the economy more broadly.

What do the Big Three do? They provide a basic financial service to investors: in exchange for a fee, asset managers invest their clients’ money in financial markets, for the most part in the stock market, or “public equities.” That sounds innocuous enough — until one understands just how much money we’re talking about.