We studied 70 countries’ economic data for the last 60 years and something big about market crashes changed 25 years ago

National economies are increasingly moving in sync and responding to the same booms and busts as a result of near-instantaneous communications and interdependent global supply chains. This is a sharp change from much of the 21st century, when economies were primarily affected by economic shocks in neighboring countries.

That’s what we found in a paper published in the journal Economic Letters, in which we calculated measures of economic correlation using data on gross domestic product for 70 countries over the past 60 years.