Most times that a country attacks another is a tragedy of the commons situation. A few people at the top will profit from the war even if most citizens from both countries lose because of it.

The country as its citizens does not profit from war. The country as its leaders sometimes it does, or at least it may do so in the short term.

I think what they refer to is that while the interests of the individual and the country almost never align, the government can work to align these interests; e.g. through tariffs on trading with that other country. By doing so, a country can reduce/remove the incentive to trade with that other country's individuals, thus aligning the interests.