'The Longest Afternoon: The 400 Men Who Decided The Battle of Waterloo' by Brendan Simms, is my fourth Waterloo book of the year.
This focuses on the King's German Legion's (KGL) defence of La Haye Sainte, which Simms claims was the key battle within the battle. Their defence held the centre of the field for Wellington long enough to allow von Blücher's Prussians to arrive & effectively finish Napoleon.
It's a well-written & researched account of the day at La Haye Sainte & does well by all who fought there, including the French.
He is very insistent about La Haye Sainte's significance, which he points out (at least three times in very similar words): "is still lost amid the (understandable) emphasis on the Guards at Hougoument, the heavy cavalry charges, Picton's death, the resilience of the British infantry squares...and finally Maitland's coup de grâce to the Imperial Guard."
He makes a good case, but as that list shows battles are more than just single incidents one after another. They are interconnected, often happening at the same time & wreathed in the smoke, chaos & terror of the day.
The importance of a single part of that battle is often hard to say without straying into counter-factuals. La Haye Sainte was clearly important but if it had fallen earlier in the day would Napoleon have won? It's impossible to say but it is worth a detailed look. And the men - on both sides - who fought there are worth remembering.
Simms does an excellent job of explaining not just the battle but the creation & make-up of the King's German Legion, individual stories from within that battle and putting the KGL into a post-Waterloo context too. He quotes Field-Marshal Lord Bramall who refers to Waterloo as 'the first NATO operation' so multi-national was the army that fought there: British, Hanoverian, Brunswickers, Dutch, Flemish and Walloon (before you throw in the Prussians).
It is good to be reminded that our history is not as separate from Europe as we might like to believe and that Waterloo wasn't won - just - on the playing fields of Eton. Not that I think this is the book's intention, just something I took from it.
Definitely worth a read if Waterloo is your thing, although it is actually as much about the trials of men in battle as it is the strategic and tactical stuff of military history. The story of Friedrich von Ompteda would be worth a book in its own right (and makes the Prince of Orange the nearest thing to a villain this book has.)