The European colonial campaigns in Africa were generally conducted by European forces with support from native troops. While European soldiers were generally more reliable, they were susceptible to diseases in tropical climates that local Africans had adjusted to, making it more optimal (less money had to be spent on medical treatment) for the latter to be deployed in Sub-Saharan environments. As such, European formations were often deployed on the continent for limited periods of time, while native units were used for longer expeditions. The powers concurred that the "African methods of warfare" were "inherently cruel". Such logic was used to justify the commission of atrocities in conflict.