/ ˈstrɒŋhəʊld; NAmE ˈstrɔːŋhoʊld/ noun
1.
an area in which there is a lot of support for a particular belief or group of people, especially a political party :
a Republican stronghold / a stronghold of Republicanism
2.
a castle or a place that is strongly built and difficult to attack
3.
an area where there are a large number of a particular type of animal :
This valley is one of the last strongholds of the Siberian tiger.