Question

What was decided at the Berlin Conference?

Answer 1

"That European nations would have to alert one another about any African territory they claimed" would be the best option, since this was at the prime era of colonization in Africa. 

Answer 2

During the Berlin Conference, it was decided that European nations would have to alert one another about any African territory they claimed.

The Berlin Conference, held between November 16, 1884 and February 27, 1885 in the city of Berlin (German Empire), was convened by France and the United Kingdom and organized by the Chancellor of Germany, Otto von Bismarck , in order to solve the problems implied by the colonial expansion in Africa and resolve its distribution.

After the Conference, all Africa (except Liberia) was divided among the signatory powers. However, Abyssinia (now Ethiopia), whose control had been assigned to Italy, resisted the invasion and remained independent. Liberia, on the other hand, was an old American colony that had achieved independence in 1847, and that was not subjected to new colonization.