As France, for instance, it's fairly easy to defend against an extended "frontal" attack in the north by England and Germany, by covering the connected zones, Burgundy, Picardy, and Brest. Fortunately I've never had to do this, but it seems harder to defend against a simultaneous attack by England, aimed at Brest, and Italy, aimed at Marseilles, on a northwest to southeast axis.
As Russia, it's relatively easy to defend against a two power attack from the west or southwest, say by Austria-Hungary, allied with either Germany or Turkey. That's because Sevastopol, the Ukraine, and Warsaw form a natural defense line. The one to fear seems to be England and Turkey to both the north and south. Then Russia is split in two directions, and easy game if one of the Germanic countries becomes a third attacker.
Has anyone had the experience of being victimized by "divergent" attacks at both ends of the Empire? Or more to the point, gone out of their way to create these kinds of problems for their opponents?