[Name] : Names of nations. The yellow name is nation which has leagued with you.
[Amity] : The amity fluctuates from 0 to 100.
The higher amity is, the more your diplomatic actions tend to succeed.
In addition, when you aim to achieve “Diplomatic victory”, amity is very important factor.
[Potential] : Potential is same as “WP”.
The lower potential you have, the more other nations tend not to take your diplomatic actions seriously.
[Revenue] : These are the each nation’s revenue per turn.

[Friendship] : By using funds you promote the friendship between two nations.
If it succeeded, +20 amity. Otherwise, -10 amity. (it doesn’t spend funds)

[League] : You suggest concluding a defensive pact to other nation.
If it succeeded, that defensive pact lasts for 6 turns.
The defensive pacts are always mutual. Therefore, if a signatory to a defensive pact is attacked, the other partner have to send reinforcement.
(If you don’t send reinforcement, you will lose the international trust.)
In addition, all provinces which two nations have will receive the +5 Econ. bonus per turn.

[Joint struggle] : You suggest concluding a pact of joint struggle to allied nation.
The pact of joint struggle asks the nation to go to war against another nation.
If it succeeded, that allied nation will send reinforcement in the battle of against target nation.
The pacts of joint struggle are always mutual too.