From a Roman History Perspective, Arabic studies is in desperate need of more scholars. Learn Syriac and get to translating. Over the next twenty years we're going to see a lot more of the Persian side of history coming out.

Popular historians are also scarce. For example, Peter Brown's famous work that unveiled the more vibrant side of Late Antiquity did a great deal to push this field, but still there are so few scholars working on, for example, the dramatic arts of Constantinople which includes, but is not limited to, pantomime performances, the ritual of the procession to the games, etc. There's also not enough scholars working on magic and performative ritual. For example, there are so many cursed tablets that have just never been translated.

Food for thought, hope this helps.

Precolonial Africa. Really, most of African history is under supplied especially with African scholars, but Precolonial is especially tough.

Part of the reason is that working on Precolonial Africa requires a mastery of material, oral, and textual sources (as relevant), besides which Africa is not just one place so you need a lot of specialized local knowledge (language is key). The groundwork just hasn't been done in many areas and subjects, in part because the idea that Africa has no history is so pernicious and persistent. This creates a feedback loop of absence: the absence of scholarship implies that nothing is there to be known or found, so nobody does the work, so there is little scholarship, going back to the old Sid Meier model of human achievement that suffused the colonial era.

Another part of the reason is that the subject is dominated by people from outside the continent, which matters in terms of skills and access. There are a few reasons why most talented African scholars in any field of history tend not to go into research, but it boils down to the legacy of global inequity. There is no money in it. The most successful Africanists I knoe from the continent all are based in Europe, North America, a few in East Asia, and Oceana. This is the only way to get the money and text resources to succeed in research; most African institutions can't afford JSTOR and its ilk, much less buy books at will. A few South African and similar places do all right but they fall behind now. The decline of History departments in SA has been stark and ugly. This has chilled a lot of serious research from those inside these countries.

A last bit is access, which goes hand in hand with the outsider phenomenon. We have to obtain research permits which take time and money, and some countries won't permit research at all for political reasons. In the precolonial case, you have to track down families and communities where you need to work, and spend time building relationships which is hard if you're foreign (it has different perils if you are not). Then you have to deal with very fragmentary records. Jan Vansina talks about some of this in Living With Africa (1994) on his pioneering work on Kuba.

So yeah, lots of roadblocks and few resources means there are very few of us. My subfield (SA in particular) is far easier to work with than most on the continent, and I am under no illusions about that. It's a huge area, 55 countries and over a billion people, wildly diverse. It's hard to categorize but there it is.

If you mean to read up on for your own benefit and maybe to help out at a place like AskHistorians? We desperately need people who do any kind of African history; history of India; we can always use more China and Japan people; history of Oceania; black history (U.S. and diaspora more broadly); modern Latin America; anything involving women and/or gender. Also, modern computer history!

These are areas in which there is fairly widespread public interest, but also very few people who interface between historical research and the public.

If you mean to study in graduate school with the end goal of becoming a history professor or other professional historian: none. There are no jobs, and there will be even fewer in the future. We need high school history teachers who can qualify to teach AP classes and "dual credit" high school/"college" classes, so students can get to uni with their requirement (if there is one at all) fulfilled and never take a university history class at all.

Most of the emerging history on the breakup of the former Yugoslavia is still driven by contempoary media sources - most of which never really reflected the realities or complexities on the ground (or the findings of the tribunals)