I've made several copyedits/minor formatting fixes; revert anything you don't agree with
"But Gascony was disproportionately important:" - to the French, the English, or both?
I could easily add 'to the English', but given that the context is "held by the English in France was Gascony in the south west. But Gascony was disproportionately important: duty levied by the English Crown" are you sure that is not already clear and that that won't be a lot of "English"?
"successful campaigns in Aquitaine and the Anglo-Gascons were" - link Aquitaine
Ah ha! Done.
"The expedition returned to Gascony on 2 December having marched 675 miles" - is it appropriate to say that a mounted raid marched?
Good point. The first three paper RSs I picked up all use it, and one meaning in Wiktionary is "To go to war; to make military advances", so I guess so.
"Despite it being clear that Breteuil could be neither stormed nor starved, John felt unable to abandon its siege" - I think it should be introduced earlier that John was besieging Breteuil.
Quite right. I thought it was. Got lost in summary style condensing and my clumsy copy editing. Now two mentions in "1356".
" horse armour is known as barding and was a recent innovation" - This needs some sort of clarification, as hadn't horse armor been used by the cataphracts been in use for centuries?
Ah, yes, I haven't said what I meant. "Plate" now specified. I have also reined in the geographical claim, although I am not sure that is necessary. "horse armour is known as barding and the use of plate armour for this was a recent innovation in Western Europe."
" the wagons may have been empty and returning to their laager in the rear," - link laager as an unfamiliar word, but it seems a bit of an anachronism to use laager, as it is derived from Afrikaans I believe
It is fairly standard in BritEng, at least in MilTalk. Tanks laagered (yes, as a verb) in laagers during and after WWII. Still do for all I know. I have Wiktionary linked it.
"Throughout the battle the experienced English and Gascon commanders were able manoeuvre and redeploy their troops in a way the French were not" - missing a word?
I don't know how many times I read straight past that. Thanks. Fixed.
"The war did not end until 1453, with a French victory." - the lead specifies the French victory, but the body doesn't
LOL! Added.
I think something is wrong with the ISBN for Hindle 1971
Good spot. I have used the Library of Congress number! *rolly eyes* Fixed.
I don't think the full dmy date is needed for Livingston & Witzel 2004 or Mitchell 2008 or Nicolle 2004
Expunged.
Image licensing looks fine, no concerns with source reliability