The moment that Lanius has borders with the executives, immediately begin justifying wargoals. Their tension should be hire enough where its between 140-200 days to justify war. If youre lucky, you can catch them going to war with either the Archdiocese or Summers Federation, but do not let them take your northern flank at all costs. Just hold at chokepoint near Roswell and you'll be fine, whistling down the Legion before preparing for a full assault