Host the Congo Conference is a decision, which gives 
Congo cores, and thus makes it possible to exist. Congo does not have any cores before the decision, and thus cannot exist before. The Congo Conference is maybe more famously known as The Berlin Conference.
It requires that the 5 provinces Kinshasa, Lunsambo, Kisangani, Irebu, and Bunkeya are unowned by the year 1880. It is possible to take as 
United Kingdom and gives them 25 prestige.
It gives Congo Cores on the 5 provinces in question and set the flags country_flag = hosting_the_congo_conference and global_flag = congo_conference_held.
Ingame text
The Congo Conference, also known as the 'Berlin Conference' was an international conference held in 1884 at the initiative of German Chancellor Otto Graf von Bismarck. The immediate consequences of the 'General Act' adopted at the conference was a formalization of the rules of engagement for colonial expansion in Africa, and the confirmation of The Congo Free State as the personal property of King Leopold II of Belgium. What will be the outcome this time around? Host the Congo Conference and the dice be cast! We should be ready to send an invitation to the other countries within a few months of enacting this decision