It is in fact a historical milestone lead by a centrist party, the United Party for National Development

https://news.un.org/en/story/2023/01/1132212

Zambia is a Southern African country nearby Zimbabwe and Mozambique

Who what when where why now?

Zambia chose to have the death penalty abolished so late because according to The Guardian, the removal of the death penalty is a positive step that marks the end of the use of a cruel, inhuman and degrading method of punishment after the last execution happening in 1997.

No party in Zambia from 1997 until now were conservative but the closest party that were and now in charge to being right of centre is the United Party for National Development which according to Wikipedia, they are a centrist party.

https://www.theguardian.com/global-development/2023/jan/09/zambia-has-killed-the-death-penalty-but-other-rights-remain-on-death-row
https://africanlii.org/article/20210624/time-end-mandatory-death-penalty-zambia
https://en.wikipedia.org/wiki/United_Party_for_National_Development