breeding ground

/B R IY1 D IH0 NG G R AW1 N D/
noun
  1. 1

    A place or region where animals go to breed.

  2. 2

    A place or institution seen as creating large numbers of a stated thing, type of person, etc.

Source: https://en.wiktionary.org/wiki/breeding%20ground, https://en.wiktionary.org/wiki/breeding-ground