Oxford University Press has a series of called Very Short Introductions. The number of pages varies but I think they're all fewer than 200 pages. I know that's a bit over your limit but 100-120 pages is longer than an article while generally being shorter than a book so it's a bit hard to hit that page range. If you have access to an academic library, you might try looking for dissertations.

I read a handful of Very Short Introductions for undergraduate classes and found they do a good job of bridging the gap between popular reading history and the sometimes dry, boring stuff academics read. They are written by experts on the respective topics and easily digestible.

Quite a few of them cover quite broad periods, for example The Renaissance: A Very Short Introduction, but here are a few specific to the 20th century you might be interested in:

The Beats: A Very Short Introduction

The Cold War: A Very Short Introduction

The First World War: A Very Short Introduction

Nazi Germany: A Very Short Introduction

Prohibition: A Very Short Introduction

The Reagan Revolution: A Very Short Introduction

Hi there anyone interested in recommending things to OP! While you might have a title to share, this is still a thread on /r/AskHistorians, and we still want the replies here to be to an /r/AskHistorians standard - presumably OP would have asked at /r/history or /r/askreddit if they wanted non-specialist opinion. So give us some indication why the thing you're recommending is valuable, trustworthy, or applicable! Posts that provide no context for why you're recommending a particular podcast/book/novel/documentary/etc, and which aren't backed up by a historian-level knowledge on the accuracy and stance of the piece, will be removed.