As Salamu Alaykum, Have you read Wael Hallaq's book on this called 'The Impossible State'? If so, what did you think.
Even though the concept of nation-state as ethnic group (such as Arabs, persians, romans etc.) was widely prevalent, the concept of "country" during the Prophetic time was never like the one we have today (i.e. fixed, unchanging physical borders etc.) I doubt you will find anything referencing "country".
the hadith in bukhari is: #2843 whoever supports (equips for battle) a warrior in the path of Allah, has himself taken part in the holy-war. whoever supports the family (left behind) of the warrior fighting in the path of Allah, has (as if) taken part in the holy-war. === whoever claims the translation is 'COUNTRY' may please furnish proof. the word is "in the path of Allah".
Is there a hadith with this wording: The beloved prophet (peace be upon him) said; “Whoever trains to fight for the sake of God to protect his country is rewarded like the one in battle, and whoever stays behind and takes care of the soldier’s family will also be rewarded” (Bukhari).