JANEK SKARZYNSKI/AFP

Russia's moves on missile defense and its decision to back out of a key arms control treaty are understandably gobbling up most of the news space devoted to Eastern Europe. But keep an eye on relations between Poland and Belarus, which claims to have busted up a Polish spy ring:

Belarus says it has smashed a spy ring which was passing information to Poland about a joint Belarussian-Russian air defence system, called the S-300. The head of the Belarus KGB security service, Dmitry Vegera, said four former Belarussian army officers and a Russian officer had been arrested.

The missile shield has clearly exacerbated relations between the two countries, but there are a host of other nettlesome issues. For months now, Poland has been broadcasting news into heavily-censored Belarus and accepting students who have been kicked out of Belarus's universities for political reasons. In their attacks on the thuggish and unpredictable Belarussian president Alexander Lukashenko, Poles frequently invoke their own legacy of Solidarity. Why does this matter, you ask? Because Poland is a member of NATO, more serious unpleasantness between the neighbors could quickly become another crisis between Russia and the West. And then things would really get interesting.