A campaign I once played

[Lord Siler]

A long time ago I've played this campaign, not much I can remember about it except that you were playing as this commander and your ally was also your rival and the side quest in some missions was to basically best your ally in defeating your enemy. So it was like you were going against an enemy while completing your ally, both the enemy and the ally were human btw, can anyone tell me what the campaign was? This has been bothering me for some time but I just can't think of the name or any more details.