Complex sentence: The failure at Nancy, and its reasons, had not escaped Jacques of Savoy, Count of Romont, who had fought under the Archduke's father-in-law Charles at the battle of Nancy.
Split into simpler sentences: The failure at Nancy, and its reasons, had not escaped Jacques of Savoy, Count of Romont. Who had fought under the Archduke's father-in-law Charles at the battle of Nancy.