Ex Uno Plura? A Decade of Convergence and Divergence among French Regions

In August 2015, France underwent a major administrative reform, which reduced the number of its Régions from 22 to 13. This paper provides an ex-post assessment exploiting the differential treatment created by the reform within an integrated empirical framework spanning Solow growth-accounting decomposition, convergence analysis with spatial econometric specification, and synthetic control methods. We document three findings. First, aggregate GDP per worker growth has decelerated from 4% in the early 1990s to 1% by the 2020s, driven almost entirely by total-factor productivity collapse. Second, regional convergence dynamics have accelerated markedly in the post-2016 period. Third, this aggregate acceleration in regional convergence is nevertheless a system-level phenomenon driven by stronger spatial spillovers between regions, and not a region-specific causal effect of consolidation itself. A synthetic control comparison of each merged region to an optimally-weighted combination of non-merged regions returns null results at conventional significance levels for six of seven merged regions. We interpret the results as indicating that the post-2016 convergence acceleration is consistent with the administrative consolidation. The reform may have enabled faster spatial integration and diffusion of productivity across regions, but the synthetic control evidence suggests it did not generate the acceleration independently.