Global tariffs converged long term, then diverged after 2018

What the study found: Global tariffs showed a significant long-term convergence from 1990 to 2020, meaning higher-tariff economies reduced protection faster and cross-country tariff differences narrowed. The study also found a clear post-2018 divergence led by the United States.

Why the authors say this matters: The authors conclude that the findings point to an important structural shift in global tariff policy and suggest that international coordination remains important for sustaining openness. They also say the post-2018 divergence signals that uncoordinated protectionism can disrupt policy alignment and increase uncertainty.

What the researchers tested: The researchers analyzed a balanced panel covering the United States, China, Japan, the European Union, and the world average from 1990 to 2020. They used beta convergence tests, which check whether higher-tariff economies lowered tariffs faster, and sigma convergence tests, which assess whether tariff differences across countries fell over time, along with structural break analysis and a difference-in-differences model.

What worked and what didn't: The beta-convergence results supported long-run alignment toward lower tariffs. Sigma convergence also showed declining dispersion, though the pace slowed after the 2000s. Structural break tests identified liberalization episodes in the European Union in 1993, Japan in 1995, and China in 1994 and 2001, while the United States showed divergence after 2018; the difference-in-differences estimates found U.S. tariffs rose significantly relative to other economies.

What to keep in mind: The tariff data end in 2020, so the analysis does not fully include the final phase of the Trump administration's protectionist measures or the broader trade disruptions linked to COVID-19. The study also focuses only on tariffs and does not include non-tariff measures.

Key points

• Global tariffs converged over the long run from 1990 to 2020.
• Cross-country tariff dispersion declined, but the pace of convergence slowed after the 2000s.
• The United States diverged after 2018, with tariffs rising relative to other economies.
• Structural breaks were identified in the European Union, Japan, and China during major liberalization periods.
• The study used beta and sigma convergence tests, structural break analysis, and difference-in-differences estimation.