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I should add I've read through Russia's War by Richard Overy and Stalingrad: The Fateful Siege by Antony Beevor. Both have been very useful and enlightening, and now I'm looking primarily for further information & sources about the importance of that battles of Moscow and Kursk.

I've also got on hand with me Bloodlands by Timothy Snyder, but I've been turned off due to its length and some bad reviews I heard.

Edit: I've also just had a read through David Glantz' essay on the Eastern Front, which covers these three battles and their status as 'turning points' - it's been very helpful, but I'm still looking for other perspectives. He argues that all three were turning points, but that Stalingrad was the most pivotal. Which historians argue otherwise?