/// <summary>
/// Gets the relation between two factions.
/// </summary>
/// <returns>The faction relation.</returns>
/// <param name="sourceFactionId">Source faction identifier.</param>
/// <param name="targetFactionId">Target faction identifier.</param>
public Relation GetRelation(string sourceFactionId, string targetFactionId)
=> world.GetRelations().FirstOrDefault(r => r.SourceFactionId == sourceFactionId &&
r.TargetFactionId == targetFactionId);