According to the earliest Arabic sources, the mid-seventh century witnessed the permanent and complete subjugation of almost the entire ancient Iranian cultural world from Iraq to Sind. Recent research has shown, however, that this smooth-and-permanent-early-conquest tradition is, in fact, largely a wishful prettification of history rather than a description of historical fact, and also heavily influenced by ?Abbbsid-era Islamic conceptions of a centralized Sasanian state. While this recent work has shed much light on the political and religious history of the northern and western Iranian lands, far less attention has been devoted to the political, military, and religious tension between Iranian relicts and the new Islamic order in the history of the Southeast, the area which today constitutes the heartland of Afghanistan. In fact, since Bosworth's trailblazing studies of forty years ago, nothing at all has been written about the ongoing wars of the S st?nt borderlands in early Islamic times. The present study will address this lacuna by examining the role of the surviving ruling dynasties of Late Antiquity, known as the Zunb ls and K bul-Sh?hs, in the provinces of Zamsndfwar, Znbulist,n, and al-Rukhkhaj (Arachosia) throughout the early Islamic period, from the beginning of the Muslim conquests in the mid-seventh century until the political disintegration of the caliphate in the mid-ninth century and the reorganization of the eastern Islamic world under the daffdrids. In tracing the ongoing importance of these kingdoms, this study will show that the survival of these Late Antique relicts constituted the most salient religious and political fact of the south-eastern borderlands throughout the two centuries of transition to Islamic rule, and a crucial element in shaping the history of the entire Islamic world. It will do so through the use of chronicles such as those of al-Ya qhbs and Khalafa b. Khayyd ; local histories including the Ttrrkh-i Scstdn, Marvaz?'s Tkr-khn?ma-yi Herat, and Zamchr ?sfiz?ra's Rawrat al-Jannat f? awssf-i mad?nat Her?t; conquest literature such as Baladhurr's Futon al-Buldtn; and the major geographical works.