What to do exactly for Diplomacy Victory?

[Yuri Bezmenov]

I wanted to finish a game with only the Diplomacy Victory with the Pilgrims.

The thing is, me and other empire (only 2 empires in the game) are in a state of peace, and I thought that was good... until I realized that I've got the 4% of Diplomacy Victory... all time. And that while I'm researching the "create an alliance". We never had a fight, and the other empire wanted to open borders with me and shared with me some resources. But nothing else.

Anyway, I have the feeling that somehow I've been doing it wrong all the game.

So, what actions makes grow up the "%" of the Diplomacy Victory? What to do in order to make that victory?