A war with Russia is a possibility, and if it ever does occur, experts agree that the US military’s globe-spanning force would clobber the Russian one in any toe-to-toe conventional fight. But modern wars seldom play out like that, and geography, politics and terrain often give one side a decisive advantage.

The incident over Ukraine has revived Cold War levels of suspicion, antagonism and gamesmanship. It also highlights the risks of a miscalculation that could provoke a direct clash between American and Russian forces.

Even if a conflict with Russia does not turn into a full-scale war, the two powers will still face off over their nuclear arsenals. Both nations have thousands of nuclear weapons, and their use could alter the world forever.

But it is important to recognize that America’s antagonists—Russia, China and Iran—are not formally allied. But they do share a common vision of the Eurasian heartland and an overriding incentive to confront the US. They may feud over Syria, Ukraine and other issues, but they also work together to undermine US global posture, shielding Iran from sanctions, shielding Russia from sanctions against the Kremlin and promoting a loose revisionist axis that seeks to push back US power.