Activists in a large city join forces to create a new organization with the goal of preserving landmark buildings that have historical importance. at first, the organization functions democratically, but over time it is taken over by three people. these leaders establish a bureaucratic structure that them to maintain control of the organization. these developments can be best explained by:

The iron law of oligarchy

Explanation:

The iron law of oligarchy is a law of all organization including those are committed to democratic ideals and practices will succumb elite the rules with oligarchy. It has been contended that organizational democracy is an oxymoron. Even the elite control makes internal democracy very unsustainable. It is also called shape the long term development of all organizations. It is a central law of an organization in labor, political parties, etc.  

you answered your own : -/