Why did Muhammad move from Mecca to the city medical

He was not able to preach Islam in Mecca, but he was able to do so in Medina.

an informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.