A direct military clash between NATO members would represent a major breakdown of the post-WWII geopolitical order, qualifying as a 'Black Swan' event. This would trigger extreme market panic, driving capital rapidly into safe-haven assets (Gold, US Treasuries). If the conflict involved Turkey (controlling key straits), Crude Oil would face a severe shock. Such an event would severely damage the credibility of the Western alliance, causing a sharp sell-off in global equities.