17 August 1992
A treaty, which effected the establishment of the Southern African Development Community (SADC), was signed in the Namibian capital, Windhoek, to replace its forerunner, the South African Development Co-ordination Community (SADCC), of which South Africa was not a member until the new treaty was signed in 1992. The structure has now grown from nine to fourteen member states.
References

Burger, D. (ed)(2002). South Africa Yearbook 2001/02, Pretoria: GCIS, p. 278.