What is Insularism?

Insularism definition and meaning on Dictionary terms:

of or relating to an island or islands: insular possessions.
dwelling or situated on an island.
forming an island: insular rocks.
detached; standing alone; isolated.
of, relating to, or characteristic of islanders.
narrow-minded or illiberal; provincial: insular attitudes toward foreigners.
Pathology. occurring in or characterized by one or more isolated spots, patches, or the like.
Anatomy. pertaining to an island of cells or tissue, as the islets of Langerhans.