A no-fly zone is considered effective if an opponent with a significant air force is denied their use in a given region. If the other opponents too have a strong air force, then setting up a no-fly zone can be challenging. The balance of power on the ground can be significantly changed by the no-fly zone declaration. A no-fly zone could be combined with other actions—such as a naval blockade or closing of a border—to stop the flow of goods and people into an area, further weakening an adversary. No-fly zones may also be established on a short-term basis to protect events going on in those areas. Another reason to set up such zones could be because the natural topography of the land is prohibitive to flying or to help protect some areas from pollution.
