Better Alliance
A simple mod that does the following:
Features:
1. No Alliance Breaking: Refusing to join war no longer breaks alliance nor vassal.
2. Friendly Diplomacy: Slightly easier to reach deals (non-aggression, alliance, marriage, region trade) with friendly factions, or factions at total war or last stand.
3. Less Strategic Threat: Halved the penalty for relationship.
Should be compatible with everything, and safe to add or remove mid-campaign.