The fate of the defense minister, Oleksii Reznikov, had been the subject of increasing speculation in Ukraine. It was the biggest shake-up in Ukraine’s government since Russia’s full-scale invasion.

https://www.nytimes.com/2023/09/03/world/europe/zelensky-ukraine-defense-minister.html#:~:text=Zelensky%20Replaces%20Defense%20Minister%2C%20Citing,since%20Russia's%20full%2Dscale%20invasion.