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The obvious question is whether the rise in borrowing has put the global economy in danger of another financial crisis. It’s impossible to know the answer. But I think there are reasons for concern.

Governments and many businesses have high levels of debt — while many middle-class and lower-income families across Europe and the United States have been struggling with slow-growing incomes. Historically, periods of extreme economic inequality, like the 1920s and the early 2000s, have been prone to financial crisis.

In an essay published this morning on Medium, Elizabeth Warren argues that the United States economy is at greater risk of a debt-caused crisis than many have realized. Obviously, Warren — as a Democratic presidential candidate — has an interest in suggesting that the economy is weaker than it appears. But she also has a track record of prophetically warning about systemic financial problems. So it’s worth giving her a hearing.

“The financial markets agree that there is a serious risk of downturn in the near future,” Warren writes. “The U.S. Treasury yield curve — a barometer for market confidence — normally slopes upwards because investors demand higher yields for bonds with longer maturities. But this March, it inverted for the first time since 2007, signaling that investors are so worried that things are going to get worse that they’d rather lock in lower rates for the future today than risk long-term rates going even lower. The curve has inverted before each and every recession in the past half century — with only one false signal.”