In your sentence, the emphasis is on A.

What they’re doing is basically backing up their argument by saying “it’s the same for war“, it’s an extension of “En amour, tous les moyens sont bons“.

It can vary on other sentences depending on how and where in the sentence “A comme B” is used.

It’s really hard to tell without a context. In some uses of comme, there’s no emphasis at all

La nuit a certainement une influence très grande sur les peines
morales comme sur les douleurs physiques

But if you want to liken thing A you’re mainly talking about to B, or broaden your point from starting context A to other contexts, you’ll usually put A first.

e.g.

Dans cette ville comme dans le reste du pays, l’argent est roi.

reads like your main point is about this city. The reverse

Dans le reste du pays comme dans cette ville, l’argent est roi.

reads like you’re either putting them on the same level, or your main point is about the country.

As a result, in

En amour comme à la guerre, tous les moyens sont bons ! Seule compte la victoire !

I would say that the author either

• Treats both equally (for instance, if the main subject isn’t love or war but victory or means to an end)
• Or was mainly talking about love