Have you ever been playing the board game Risk, found that a competitor only has Iceland and Northern Europe, but has three risk cards coming next turn? What do you do? You wipe him off the map as quickly as possible, of course, before he has a chance to use them and become something more threatening.

Friday, we learned that the Nusra Front in Syria had attacked a U.S.-trained opposition group, known as Division 30. While U.S. officials seemed surprised by this development — "This wasn't supposed to happen like this," one former senior American official told the New York Times — they shouldn't have been. Nusra's motivations were clear, and they were pretty open about them. From the New York Times:

The Nusra Front said in a statement on Friday that its aim was to eliminate Division 30 before it could gain a deeper foothold in Syria. The Nusra Front did much the same last year when it smashed the main groups that had been trained and equipped in a different American effort, one run covertly by the C.I.A.

There are many reasons why supporting rebels in civil wars is deeply morally problematic, but one seldom-discussed reason is that doing so makes them targets. Division 30 might be small relative to other players, but its existence represents the interests of the most powerful nation on earth. Not surprisingly, the al-Qaeda-linked Nusra front would want to eliminate such a group as quickly as possible before it turns into something more threatening.