Why did the early ottomans switch from single partner marriage as a way of gaining land and power to the system of using slaves concubines (harem) as a way to produce many heirs? Also when? I'm asking on behalf of my middle school SS teacher girlfriend in an effort to show her how cool this subreddit is (she loved the recent prostitute post). Lemme know any sources you might have!
For example she says Osman the first married a sheik's daughter in order to gain land (and she's pretty sure that he only married her)
To the best of my knowledge, and with reference to the work of Kafadar:
Ottoman family politics changed significantly around the reign of Mehmed II (1432-1481) Arranged marriages were useful politically, and Christian princesses were not necessarily expected to convert to Islam. I know relatively little about this period, but I'd actually be pretty surprised if these were monogamous partnerships as we'd understand them. Succession was initially 'survival of the fittest': for example, when Mehmed II's father died, he raced back from his local base of power and had to kill his (19!) brothers. He was (I believe) the last to do this. Afterwards, the oldest brother was heir, and other brothers were either murdered (to prevent opposing factions using them) or imprisoned in the palace. [this is simplified somewhat].
After 1520 it was the exception rather than the rule for a dynast to marry. There were no more marriages to Christian women, and after Mehmed's grandson, no more to any neighbours, Muslim included.
It isn't absolutely clear why these changes came about. There are obviously advantages to both political marriages and the harem system. Apart from anything else, the harem system, and the lack of heirs of the sultan's killed or imprisoned brothers, meant that no landed and dynastic aristocracy could develop through intermarriage with the sultan's dynasty. Additionally, it was under Mehmed that Constantinople was captured (1453) and the first legal codification (outside divine law) in the Islamic world was set up. Kafadar has argued that it was under Mehmed that the shift from principality to empire was made. The central administrative apparatus that Mehmed set up established a closed court, distinct form the open court of the Gazi chief. My interpretation is that, with Mehmed's conquests and the setting up of a more sophisticated administrative apparatus, harems seemed a more exclusive and tidier way to organise the dynasty. Plus, of course, few of the Ottoman's neighbours could hold a candle to the reaches of the newly expanded Ottoman empire.
I'd be interested in anybody else's interpretations!