Many bacteria are extremely aggressive. They assemble poisoned molecular spears to stab neighbours, they release protein machines that punch holes in competitors and, moreover, some cells will commit suicide in order to launch their attack. While there is a large literature on the evolution of combat and competition in animals, this has focused on why animals are generally reluctant to fight. The evolution of extreme aggression in bacteria, therefore, challenges our current understanding of competition in biology. My project has been developing bacterial warfare as a model for competitive behaviour by asking three key questions that each build in complexity: 1) Why do weapons evolve? 2) What tactics do bacteria use during combat and why? 3) How does ecological complexity influence the value and use of weapons? These questions are important for our fundamental understanding of bacteria and conflict, but also for the growing recognition that we need to be able to predict when and how particular bacteria will invade and grow if we are going to manage the human microbiome, which is so central to our health and wellbeing. We are aiming to show that, understanding the microbiome, will need a new focus on the evolution, and ecology, of bacterial warfare.