Cause of the synchronized 2018–2019 modularity peak and collapse

Determine whether the synchronized peak and collapse in modularity around 2018–2019 in the ego-networks of China, Great Britain, and the United States was caused primarily by exogenous geopolitical shocks, endogenous network changes, or a feedback between the two, and identify the operative causal mechanisms.

Background

The authors observe an unexpected, sharp, and synchronized peak followed by a collapse in ego-network modularity for the U.S., Great Britain, and China around 2018–2019. This was not predicted by their structural framework and suggests a system-wide disruption.

They outline possible explanations—geopolitical shocks, endogenous network dynamics, or both—but explicitly state that their data cannot adjudicate among these possibilities, calling for further study.