Last Stand "A new threat is rising"

So I recently watched the Year One video again (Link here for refreshers: https://www.youtube.com/watch?v=c_qUtFkdPEk ) and I am wondering. Where is this new relentless threat mentioned in the Last Stand part? Rogue Agents aren't new so I wonder, was Last Stand suppose to be something totally different then a game mode or was it all just fluff like Underground's explanation?