Interesting topic.
Though keep in mind that it might be states being at war with each other, it's usually (but not always) individuals or companies that are trading.
The interests almost never align.
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But it's much more than that I think: when the stuff you sell to the other side can easily be substituted, from another supplier, domestically or by changing to ways that get by without, where's the benefit of stopping trade? Those 0.5% the other supplier has been more expensive (if it even is, might very well have just been inertia keeping them buying from you) won't meaningfully harm their war effort.