Belarus is key here. If Belarus were to be integrated into Russia, the West’s defense of Poland, which houses U.S. troops, becomes much more difficult. But if Belarus were to switch to the West and NATO troops were deployed, the defense of Smolensk and even Moscow would be difficult. The Russians have an initiative underway to integrate Belarus with Russia, but in recent weeks, Belarusian President Alexander Lukashenko has been signaling an interest in maintaining good relations with the West.
Belarus is a flashpoint on this frontier. Lukashenko wants to maintain its free movement, Russia wants to lock it in, and Poland does not want to see more Russian troops on its eastern border. For Russia, settling the Belarus question is a vital matter. For Poland, even with more limited, though quite good, forces, this would cause a fundamental crisis and involve the United States. And this issue is moving to some sort of decision. The West does not want a shift, but Russia doesn’t trust the West and claims that its absorption of the Baltics into NATO already violated Moscow’s understanding with the West.
So there has been significant tension between Poland and Russia over Belarus. Belarus is important enough to Russia to consider military action – and the two countries have staged huge war games near Poland’s border in the past. Poland may see any such move as indicating war, if not now then later.