On Sep­tem­ber 21, the inter­na­tion­al day of peace, ter­ror­ists killed dozens of civil­ians in a shop­ping mall, includ­ing chil­dren and preg­nant women. Most vio­lence in the world is no longer in the news. Drugs mur­ders in Mex­i­co, gueril­la wars in Con­go. Vio­lence always moves in cir­cles. After the attack in Nairo­bi, the dan­ger is that …