Stephen Biddle’s published an essay on the Ukraine War in Foreign Affairs. Titled “How Russia Stopped Ukraine’s Momentum: A Deep Defense is Hard to Beat,” it argues that for now, the best explanation for the failure of Ukraine’s summer offensive is Russia’s adoption of an orthodox defense-in-depth of the kind that has historically been very hard for attackers to break through. The essay then draws implications for the future of the Ukraine war and for U.S. defense planning. 

You can find the essay at: https://www.foreignaffairs.com/ukraine/how-russia-stopped-ukraines-momentum.