Confederation tactics can be separated into five different categories

1. Confederation through diplomacy
2. Confederation through diplomacy and war
3. Confederation through beating enemy faction lord
4. Vassalage and Subjugation
5. Confederation through events

1. Confederation throught diplomacy

This apply´s to the following races:

• High Elves
• Lizzardmen
• Dark Elves
• Skaven
• Dwarfes
• Greenskins
• Vampire Counts
• Norsca
• Bretonnia
• Wood Elves

This is the most basic way to confederate within your own race. For that you will need:

• High reliability
• Relashionship of +100 in most cases
• Stronger overall army-rating compared to confederation target

Additional factors like …, will increase the likelyhood of a confederation:

• The confederation target is in a loosing war
• The enemy faction has a stronger army-rating
• An army of confederation target has been recently wiped out
• Legendary Lord of confederation target has been wounded
• A settelment of confederation target is beeing threatened by a nearby army

This factors like …, will decrease the likelyhood of a confederation:

• The confederation target is at peace
• The confederation target has a strong economy.
• The confederation target has a equal or stronger army-rating then yourself
• The confederation target does not like you or is neutral
• Your reliability is low
• You have an military alliance with confederation target.

Benefits of confederating throught diplomacy:

• You get the AI army most times without any damage.
• You can ally your confederation target and use him as a bufferstate or support.
• Your confederation target builds up your settelments for you to tier 3+, especially on legendary difficulty they do that very fast.
• You can have an trade agrenment which gives you required items for crafting and additional gold income.

Downsides of confederating throught diplomacy:

• Depending on your confederation target it is difficult to get them into an war, since it requires a military alliance.
• It is sometimes luck bases. Most minor factions are more devencive in their nature, therefore they dont tend to leave their region.
• If the confederation target is surrounded with allies and has good economy, it will take a lot of effort and gold to get a confederation.
• Some minor factions have a basic dislike for your own race which makes confederation very difficult. For example Karak Hirn.

2. Confederation through diplomacy and war

Mercy the mad has a nice example on how to achieve this:

3. Confederation through beating enemy faction lord

This apply´s to the following races:

• Greenskins
• Norsca

Confederations throught beating enemy lord is possible throught scripted event, therefore only possible for Greenskins and Norsca factions. To figure out what the faction leader of a minor faction is, go to diplomacy screen and check the faction leaders name. The minor faction leader is unkillable. If he is not wounded you will find him on the campain map.

Benefits of confederation throught beating enemy faction lord are:

• Confederations are instantly possible.
• Factors like reliability do not matter.
• Factors like army-rating do not matter.
• Factors like confederation target does not like you, does not matter.
• You do not have to kill enemy faction lord in order to confederate.

Downsides of confederation throught beating enemy faction lord are:

• Any sort of alliance or agreenment with target faction will hinder you from instantly declaring war on target faction lord or you will loose reliability.
• You will have to wait 5 Turns for a legendary lord to recuperate if killed in battle.
• You might kill enemy heroes which can be aquired throught normal confederations.

Vassalage and Subjugation

This apply´s to the following races:

• Tomb Kings
• Chaos
• Norsca

Specially good is vassalage for tomb kings since they cannot confederate other Legendary Lords into their own faction.

Making someone your vassal is most time very difficult. They have to be beaten up and loose almost all of their settelment.

A way around is to pay them a lot and threaten their settelments.