Leadership bonus of Chief Warlord applies to all units of their capital.Erf-b1-p041a Having the Chief Warlord in the same hex adds another bonus. Units in the stack led by Chief Warlord get yet another bonus.Erf-b1-p113
"Leadership" can also refer to a either a single leader or group of leaders such as Warlords or Casters. Gobwin Knob sought to target or "hit" the leadership of the Royal Crown Coalition to deny RCC forces leadership bonuses. They were successful when they hit RCC Leaders Duke Nozzle and the Blue Warlord.