Even as Russia claimed to be pulling back troops from extensive military exercises that had sparked fears of invasion, the Kremlin sent a reminder to the world that it has one of the world’s biggest nuclear arsenals, by announcing drills of its nuclear forces for the weekend. The muscle-flexing overshadowed Russian offers this week of continued diplomacy to defuse the Ukraine crisis.

NATO allies are also flexing their might, beefing up military forces around eastern Europe, but insist the actions are purely defensive and to show unity in the face of Russian threats.

The U.S. announced the $6 billion sale of 250 tanks to Poland, a NATO member that has been occupied or attacked by Russia over past centuries. Announcing the deal, Austin said Russia’s military buildup had only reinvigorated NATO instead of cowing it, as Moscow had hoped.