After a fiery speech on Monday, Russian President Vladimir Putin sent Russian troops across the border into Ukraine’s breakaway regions that make up the Donbas region. Western nations are reacting by imposing sanctions on Russia, with Germany going so far as to stop the certification of the NordStream 2 natural gas pipeline that Putin had hoped would deliver fuel to Europe, bypassing Ukraine.So is this move a prelude to a wider invasion? Or has the invasion started? The Globe’s senior international correspondent, Mark MacKinnon, discusses the role of diplomacy now that this conflict has moved into a more inauspicious stage.