All robots believed that humans had become extinct all at once on 7th December, 2053 during the Great Power Failure. Nobot knew the reason and nobot had bothered to ask. After all, robots were not very good thinkers, they just obeyed orders. But ever since the death of the humans, they had no one to take orders from, purposelessly wandering. Atleast until the great Microbot 1047 came along. He put forward nearly every idea in the Robotic Age. He suggested the idea of creating and programming defense units. And he was the one who gave the idea of waging war on the Beasts. The Beasts were the assorted collection of mutants and by-products of evolution that existed outside of the Tower. The Tower had been the original place of respite for the humans against the rapidly changing and hostile environment around. After their demise, it became the robotic base of operations.
The idea of war on the Beasts was probably based on some immutable robot logic, however weird it was. The purpose being to glorify human creations by destroying others. Soon enough, a full-scale war was raging by the year 2058, which was widely known as the Beast- Machine War or B.M.W.