The McDonald's Theory of Conflict Avoidance argued that no two countries with McDonald's restaurants had ever gone to war. The serious underlying point was that advanced capitalist economies tend to avoid direct armed conflict because it's bad for business.

The Russian invasion of Ukraine has dealt that theory a potentially fatal blow.

The question is whether Russia counts as an "advanced capitalist economy" and if so, for long will it continue to qualify as such.

More broadly, the share of the global economy attributable to primary industries like mining and agriculture has been declining for decades as has that of manufacturing, services are where it's at. That's why China is pushing to become a service-based economy.

That implies that natural resources have become relatively less valuable and that it's generally cheaper to buy them than to go to war to obtain them. That's true even if you're a private company and can get a government to do the actual war fighting for you.

Take a look at the purported resource wars of the past 20 years:

- no oil pipelines were ever built across Afghanistan;

- Virtually all the oil contracts issued in post-war Iraq went to Iraqi, European or Chinese companies;  

- Syria and Libya had both opened up their oil and gas industries to foreign investors prior to the civil wars in those countries so the resource war theory holds the west started wars to get something they already had.   

I suspect simplistic "Donbas has gas fields" theories about the war in Ukraine are equally invalid.