Which of the following decisions made by European powers led to conflict in post-colonial Africa?

When the nations of Nigeria and Cameroon went to settle a border dispute in 2002, in which both countries claimed an oil-rich peninsula about the size of El Paso, they didn't cite ancient cultural claims to the land, nor the preferences of its inhabitants, nor even their own national interests. Rather, in taking their case to the International Court of Justice, they cited a pile of century-old European paperwork.