After the Landsmeet, when you visit Redcliffe, you're locked into seeing the main story through to its end.
When you arrive at Redcliffe, you'll discover it's been attacked by Darkspawn. It's not necessary to clear the village of them since the village is already evacuated. Your next objective is to reach and defend Redcliffe castle.
1:04 -- Castle Courtyard Battle
Most of the Darkspawn involved in this fight are weak. The only real troublemakers are a Hurlock Alpha, two Emissaries, and an Alpha Ogre. Once every Darkspawn is dead, head into the castle to learn that your army must march for Denerim.
2:58 -- Riordan Announces that the Horde is heading to Denerim
6:23 -- Riordan tells the secret to killing the Archdemon
