Historical clue formulations

• Country bordering Chad and Benin — 2026-08-19
• Country of 180+ million people that has never participated in the Winter Olympics — 2016-11-26
• OPEC member — 2008-09-05
• Neighbor of Chad — 2007-02-25
• Home of Literature Nobelist Wole Soyinka — 2005-11-18
• Its capital is Abuja — 1999-09-30
• African member of OPEC — 1999-09-14
• Neighbor of Cameroon — 1997-01-25
• OPEC member — 1996-02-25