I studied International Studies and Religious Studies in uni where most of my research was focused on Islamic militant groups in the present day. Consequently my education was very Sunni focused and given that my professors weren't incredibly familiar with the Shi'a the limited forays I made into Shi'i Islam and Iranian Twelver Shi'ism in particular were basically independent affairs.
For my education the theological history was less important than more recent developments and doctrine (mid 1800s to the present) and so while I have knowledge of the broad strokes of early Islamic history and more specialised knowledge of recent history there are some gaps in the middle.
Essentially I had been taught that the Sunni-Shi'a division dated back to early Islamic history but I've heard a few different places that there are suggestions that Shi'i Islam as a distinct entity doesn't really arise until the Safavid establishment of a distinctly Shi'a Persian state. I was wondering what the specific arguments are for this view and some reading material if anybody has any.
It's not really an argument for or against, it's a historical fact that Twelver Shi'ism really only came into prominence with the Safavid conversion of Iran to Shi'ism. Before that, although Shi'ism existed, it was not primarily Twelver Shi'ism and did not have an intertwined relationship with Persia.
As a bit of background, there have historically been three big branches of Shi'ism. There's the 12'ers, the 7'ers, and the 5'ers. Also known as the Imamis, the Ismailis, and the Zaydis. For the bulk of Islamic history, Zaydis comprised the majority of Shi'ites. The Zaydis are the closest Shi'ite branch to Sunnis. The next big ones were the Ismailis who are most famous for the Fatimid caliphate. These are the farthest away from mainstream Sunnis in terms of belief. The last group, the Imamis, are what are today synonymous with Shi'ites. This is the branch with the doctrine of 12 imams and what we think of when we say Shi'ites.
The Safavid conversion took place for an almost strictly political purpose-to establish an independent state from the Ottomans. As the Ottoman sultan was the caliph, even more powerful Sunni states had to at least pay nominal allegiance to him. Shah Ismail I wanted to make an independent Persian-Shi'ite state from the Turkish-Sunni Ottomans and this was a perfect way to do it. I can't comment on whether he sincerely believed in the superiority of Shi'ism or just found it politically expedient, but in either case, he zealously enforced the conversion and in one generation, transformed the Safavid kingdom into Shi'ism.
So to answer your question....yes and no. Shi'ism existed centuries before the Safavid period but the intertwining of Shi'ism and Persia and the modern manifestation of Twelver Shi'ism can be traced back to earlier than the Safavid period.