Friendship has expired. No option to renew
Solution 1:
The friendship may have expired, however, I have an alliance with Kongo. This is like a higher level of friendship. So once the alliance expires, the friendship and or alliance options will show.
The option is not showing because I am in an alliance.
Alliance is like Best-Bestest-Friends and is a trade option. It is not a defence treaty.
Why it is in a different spot to declaring friendship, I don't know. Should I exchange uranium for your alliance?