Books. Read books. There is a Askhistorians booklist and since you are interested in China Harvard's "History of Imperial China" series is just for you. Three of them is in the this subreddit's booklist too.

There's no specific order you must follow. Pick up a book that has a hefty bibliography and start reading. If there is something you find interesting in the bibliography, find the cited resource and continue (if possible, with Asia specifically, a significant portion of the scholarship is written in Chinese, Japanese, etc. and is not accessible in English.)

There are a great many resources about Asian history. Harvard's "History of Imperial China" series is probably the best, however, the series is quite long (6 volumes of 300 pages or so.) It's a good resource, and you'll definitely learn a lot from it. But, it's a daunting task to get through them. If you like reading, definitely start there.

Two favorites of mine: (1) "The Economic History of China: From Antiquity to the 19th Century" (Richard von Glahn). As the title suggests, it is an economic history. (2) "The Great Divergence..." (Pomeranz). The Great Divergence is written for an academic audience, but it is accessible, it just might take a while to read. Should you decide to read it, and find something interesting, there are plenty of footnotes and an extensive (and I mean an extensive) bibliography. (3) "Why Nations Fail" (Acemoglu and Robinson). "Why Nations Fail" does not cover China in any great depth, but is a good general resource.

You'll note during your studies that during the 18th and 19th Centuries, China fell quite behind economically. "Why Nations Fail" and "The Great Divergence" present two mainstream and highly influential theories in economic history: institutions and geography. I highly recommend reading both books and paying close attention.

In "Why Nations Fail" a country's economic, political, social, etc. systems stagnate because there is something wrong with their institutions (which, can be broadly defined as the "rules of the game"). The argument, with respect to China, goes something like this: China had poor institutions (empirical), societies with poor institutions stagnate (theory), China stagnated (empirical.) However, in "The Great Divergence", Pomeranz argues that China's institutions were comparable to Europe's meaning that the cause of the Great Divergence between Europe and Asia cannot be institutional in nature. He then argues the reason is geographical, namely, Europe (and specifically Britain) had (a) access to coal and (b) extensive overseas markets. So, China's divergence came about because they lacked the necessary geography to fuel industrialization.

If you wish to get somewhat caught up with the recent economic scholarship and debates (these should not be your starting place):

"Chinese History in an Economic Perspective" (Edited by Rawski and Li), "From Divergence to Convergence: Reevaluating the History Behind China’s Economic Boom" (Rawski, Ma, and Brandt), "China‘s Economy and Global Interactions in the Long Run" (by Rawski). "Wages, Prices, and Living Standards in China, 1738-1925: in comparison with Europe, Japan, and India" (Allen, et al.) "The Fundamental Institutions of China's Reforms and Development" (Chenggang Xu). "Markets in China and Europe on the Eve of the Industrial Revolution" (Shuie, Keller). "Marketing and Social Structure in Rural China" the introduction and parts 1 through 3 (William Skinner). If you feel so inclined, I have heard his book "The City in Late Imperial China" is excellent, although I have not gotten around to reading it.

To make a note about the works by Skinner specifically: unlike other economists, Skinner took a regional and cultural approach to the study of Chinese economic history. Each area in China had a specific set of goods and services available. He meticulously maps out how China's history is defined not by overall, grand, macroeconomic cycles, but rather by regional and local cycles.

Bottom line: read books to start, if there is something interesting in the book, find the citations. Books generally present a broad overview, paper's (much of the time) comment on specific phenomenon. Good luck.

Aside from textbooks and books, listening to podcasts is a way I learn history passively.

Textbooks. You can usually find them secondhand for fairly cheap and they can get wonderfully specific

Follow-up question, is Hsu still considered a decent source of information? Or is he hopelessly outdated?

I think that before you dive in (area studies being a mine-field for the uninitiated and the world wars being vast beyond any other subject upon which man has touched pen to paper -- the Yad Vashem library, which holds titles related to the Holocaust, alone has something like 150,000 books) you would be best with first with the basics. I'm not an Asia specialist, but a Second World War historian. So, i'll leave it to others (and there has been a great post already) to do that and stick to what I know.

OK. So, the best good and mercifully short book on the Second World War is -- Norman Stone's, World War Two: A Short History.

I also really like, as a good way into the subject the dated but still worthy -- Mark Arnold Forster, The World at War (this book accompanied the brilliant 1973 BBC documentary -- easily the best history TV programme ever broadcast bar none)

Also good is: Philip Warner's, World War II: The Untold Story

If you want a meaty yet very readable book designed for a mass audience try -- Max Hastings, All Hell Let Loose.

For a scholarly, yet brilliantly accessible book -- Richard Overy, Why the Allies Won.

If you're also interested in the social/cultural/psychological impact of the war see the very funny (and very serious) -- Paul Fussell, Wartime.

I could recommend some First World War books, but I fear that they might be a bit specific to British social history during the war and you wouldn't be too interested at this juncture (I only read about the First World War for work, so none of the fun books like above).

Another thing you should keep in mind:

University and college professors are good sources. These people have devoted their life to studying history. Don't be afraid to send them an email with questions (try to keep it short and specific): the worst that happens is they ignore it. However, in my experience at least, professors really, really love when people ask questions about subjects they are passionate about and will take 5 minutes to respond. Of course, as should be expected, many won't respond.

For Korean History, check out "A History of Korea" by Kyung Moon Hwang. It's a very brief overview of the highlights of Korean history (which stretches back 5,000 years!). Each chapter is between 5 and 15 pages and it's written in a very easy and accessible way. You can power through the whole thing in a few hours if you really felt like it. I recommend it just as a way to get your feet wet with Korean history. There are a lot of sources listed in the back that you can follow up with.

Personally, I'm interested in Korean history from the late 19th century which is completely tied together with Japanese and Chinese history. The first Sino-Japanese War was fought in and over Korea and it began over Chinese intervention in Korean domestic troubles. If you're really interested in this part of the world, it's a good idea to read sources from China, Korea, and Japan. Even today, the three countries are fighting over their history so you'll see some subtle and not so subtle differences of interpretation.

A History of Korea by Michael Seth is a great college level textbook that covers the entirety of Korean history in more depth than Hwang's book, but it's still not comprehensive.

The Coldest Winter by David Halberstam is a great text on the first year of the Korean War from the US perspective. Scorched Earth, Black Snow by Andrew Salmon is the same thing except from the perspective of the British/Commonwealth troops. I'm leery of some of his sources though - he cited a wikipedia article! It's still a good read.

The Park Chung-Hee Era by Kim and Vogel is a solid overview of the 60's and 70's and the Miracle on the Han. Park Chung Hee and Modern Korea by Carter Eckert is a more critical look on Park - the photo on the front is of Park in a Japanese Imperial Army uniform, an image that he and the conservatives of Korea don't want people to see.

My favorite niche books are:

Korea on the Brink by John Wickham. He was the commanding general of US Forces Korea in 1979-1980 when President Park was assassinated and Chun Do-hwan staged a coup. His book talks about the day of the assassination, the coup, and all of 1980 with Chun's maneuvering.

Low Intensity Conflict in Korea 1966-1969 by Bolger. It talks about North Korean provocations during what's been dubbed the Second Korean War and how the US and Korea responded.

A MiG-15 to Freedom by Noh Kum-sok. The author was a North Korean pilot who defected at the end of the Korean War. By defecting with the plane, he was given a huge cash reward and he resettled in the US.

There are loads of other good ones, but these are the ones that I really enjoyed.