The 1851 book "The Fifteen Decisive Battles of the World"[0] and its ilk is likely what the author refers to when talking of "decisive battles where popularised in the 19th century".

It is pretty obvious that single battles hardly determine long war outcomes, but it's a pretty attractive idea that a kingdom can be lost for want of a nail and all that.

[0] https://en.wikipedia.org/wiki/The_Fifteen_Decisive_Battles_o...

Thanks for the link. I had often heard of the importance of the battle of Marathon, but couldn't remember its provenance.

Here's an interesting excerpt from the Siege of Orleans though:

the struggle by which the unconscious heroine of France, in the beginning of the fifteenth century, rescued her country from becoming a second Ireland under the yoke of the triumphant English.

That's quite a statement from a 19thC English man.