In the beginning, he understood, humans had built a lot of robot soldiers. Technically there had to be some earlier beginning where someone or something built humans, and so on ad infinitum, but Uncharles felt that was of diminishing relevance and needlessly metaphysical.

Why humans had built so many robot soldiers was unclear, although the robots themselves had a variety of theories to justify their existence. Uncharles heard that human soldiers were less capable of making war than robots, or else less willing and reliable than robots. He also heard that other humans elsewhere had built robot soldiers, and the local humans had then had to build their own to avoid there being a robot soldier gap.

Nobody seemed to ask why soldiers at all. Apparently the existence of soldiers was a fundamental given in their cosmology.

— Service Model by Adrian Tchaikovsky