What is the difference between national park and a wildlife sanctuary?

The main difference is what government (or non-government) agency manages the land and its resources. Each agency has different priorities as mandated by their organizing legislation. National parks can be wildlife sanctuaries, but a sanctuary is not necessarily a national park. A sanctuary may be set aside by government agency or private group or individual. National parks have specific legislation on the federal level and follow certain laws.

The National Park Service manages U.S. national parks, which happen to be wildlife sanctuaries. Wildlife sanctuaries may be managed by a number of other agencies, state, local, federal, non-government organization, or private interests.