Nigeria, Sept. 16 -- As the United States marks the 25th anniversary of the 11 September attacks, one of the most important lessons from Africa is that terrorist threats rarely begin with an attack on the United States.

They begin earlier. When armed groups find recruits, develop financing, move through weakly governed areas, gain access to technology, intimidate communities and establish relationships across borders.

That is the setting in which the Deputy Commander, United States Africa Command, John Brennan Jr., views Africa's current security environment.

Mr Brennan, a US Army lieutenant general, is a three-decade veteran of special operations, with deep expertise forged in counterterrorism and irregular warfare. His position gives...