[quote]What happened exactly with the Prometheans and like the knights and stuff. Like why did they go from knights to soldier?[/quote]Knights and Soldiers are separate entities. The Soldiers are an Armiger platform created for the Human-Forerunner War. [quote]Do we have any idea what installation that Halo was in the legendary ending to H5?[/quote]It's not Installation 03. [quote]I was confused about Cortana's plans to control the galaxy. What were they exactly? [/quote]Send the Guardians to various star systems and subjugate the various species of the Milky Way. Those who wouldn't comply would be destroyed/Composed. Essentially, she completed the Reclamation and now holds the Mantle of Responsibility with the other Smart AI's who joined her. [quote]Were Guardians ever mentioned before Halo 5?[/quote]No, but given what their purpose is, there was definitely a place in the lore for them.

Guardians were hinted at in previous halo games, when you died of suicide or some other mysterious occurrence it would "Killed buy the Guardians" And the Soldier is just a lower rank of Promethean, they have way less functions than a Knight does