This sounds like a difficult project; you have the entire continent of Africa, and there were many wars in the 20th century.
Perhaps the United Nations, or some sort of think-tank organization (Council On Foreign Relations; Center For Strategic and International Studies?) has some statistics.
I'm not a Modern Warfare expert, but here's all the 20th / 21st Century African Wars I could think of:
Algeria (insurrections against the French and later by Taliban like insurgents, if you include insurrections as a "war")
Libya v. Chad
Ethiopia v. Somalia
Sierra Leone (Civil War, if you include civil wars; I'm not sure if they went to war against Liberia?)
Liberia (Civil War)
1960's Congo insurrection against Belgian Colonial Rule
Mau Mau Kenyan Rebellion against British Rule
Rhodesian Civil War
Angolan Civil (Angolan insurgents v. Portugal Colonial Rule) and Portuguese Guinea Civil War
South Africa v. Angola
1950's invasion of Egypt by the U.K. and France
Somalian Civil War & U.S. Intervention in 1990s
Rhwandan Civil War
Sudan Civil War and Darfur region