Hanno The Navigator's Ability Question

[Leefizzy]

I've noticed that you get the Explorer unit after you find 3/4 landmarks so far, how does the Offer a Tribal Alliance to 1 Tribe happen, all I see is the default alliance option that you get when your Leader is a Diplomat.
Is it when you find every Tribe in the game?

 

[FluffybunnyMohawk]

When you select your leader you will see 2 Tribal Alliance missions. One is the standard diplomat mission, which requires Peace with the Tribe and costs 400 training. The other is Hanno's special mission which only requires Truce and costs 200 training.