The relation between these is that both of them go along with agriculture and societies with high-density populations.
With agriculture, populations become more dense. When this happens, institutions of society must arise. These institutions (like government and religion) help make it possible for the larger populations to live with one another in peace. The larger populations and the social institutions make the agents of conquest possible. The larger populations allow for germs to develop. They also make it possible for technology to be invented. The social institutions make societies more able to use the technology to conquer other people.
In these ways, institutions of society and agents of conquest are related because both are results of agriculture and because the institutions of society can help to produce the agents of conquest.