I am trying to understand the US commercial aviation industry. Assuming that slots are available, are US airlines permitted to fly to and from any US city they want to? Or are there limited permits issued by each city/state that limits the number of airlines that can serve an airport/city/state? For example, if I start an airline based in New York, is it simple to get permission to fly between San Francisco and Anchorage (assume that slots are available)? Were there any restrictions before the Airline Deregulation Act of 1978?