Merging datasets

hello
i'm trying to merge two datasets but I'm not sure if what I'm trying to do (which is not working out) is even correct or possible.

I have a dataset measuring sexual violence in conflict and one which measures female combatants in conflict. I now want to add the variable that measures female combatants in conflict to the dataset of sexual violence.

i tried merging them by the common variables country, and conflict duration but stata tells me that " variables conflictdur country do not uniquely identify observations in the master data
r(459)"

this is what i did so far:

use wood_thomasJPR_replication12.dta, clear

rename duration conflictdur

sort conflictdur country

save wood_thomasJPR_replication12.dta, replace
clear

***********

use Repl2_Cohen_Nordas_JCR.dta

sort conflictdur country

save Repl2_Cohen_Nordas_JCR.dta, replace
clear

***********

use Repl2_Cohen_Nordas_JCR.dta, clear

merge 1:1 conflictdur country using wood_thomasJPR_replication12.dta, keepusing(female_combat_binary) keep(match master)
drop _merge


I'm actually just interested in adding the variable "female_combat_binary" to the "Repl2_Cohen_Nordas_JCR.dta" dataset.

Thanks for your help!!