Greetings! What an interesting bit of the past you've decided to read up on, and it can be easy to see how one might feel a tad daunted by the sheer amount of books and other secondary literature on the past 100 years of our world. Whilst I highly recommend that you check out the AH booklist for any reading recommendations on the 20th century within specific countries or for specific events, here are a few books that I can recommend for a good overview of the past century and a bit:

• The Age of Empire 1875 - 1914 by Eric Hobsbawn: This book is a tad old (1987) but it remains a popular favourite of reading lists. Hobsbawm is incredibly in his writing, preferring to look at the wider trends in social, political, and economic history over the course of the late 19th to early 20th century. His writing style is engaging, the sourcework is good (if at times lacking engagement with primary sources), and the journey that he takes you on throughout the dawn of the 20th century and the seminal tragedy of the First World War is an enjoyable yet informative one. Highly worth a read, and a great starting point for the next book on the list...
• The Proud Tower: A Portrait of the World Before the War, 1890 - 1914 by Barbara Tuchman: This book is even older than Hobsbawn's (1966), and consists of a collection of essays by Tuchman about the intellectual, cultural, and social state of Europe before the First World War. Definitely a more specific and narrow work, but one which is great as an add-on to Hobsbawn's book above. Mind you, this book does require a fair bit of background knowledge, as it does not always explain the political or global context in which the social developments occurred. Nonetheless, it is a great "window to the past" if a book can ever be called as such, to a time before the 20th century really became a rollercoaster of tragedy and triumph.
• The First World War: A Very Short Introduction by Michael Howard: Howard's contribution to the Oxford Press' Very Short Introduction series is a great all-in-one overview of the causes, course, and consequences of the First World War. It does not focus on one particular country or any particular event, but provides an excellent view of the "scenery" if you will. The sources and further reading at the end are also a great bonus to the book itself, and it played a major role in sparking my heightened interest for the First World War as an area of history.
• The Age of Extremes: The Short Twentieth Century, 1914-1991 by Eric Hobsbawn: Returning to Hobsbawn once again, this publication follows on from The Age of Empire but is far more political and social in charting the developments of the twentieth century. Mind you, Hobsbawn does not proceed in chronological order, but rather looks at wide sweeping political and social "aspects" which are then investigated through specific cases which occurred in the 1900s. Still, a rather good work overall (one I just finished reading, and a rather fun read it was).
• To Hell and Back: Europe, 1914 - 1949 by Ian Kershaw: Another book which I finished just recently (about two weeks ago or so), and obviously is a tad more narrow in its scope than Hobsbawns works (focusing on Europe before, during, and after the two World Wars). The focus here is political as well, but unlike The Age of Extremes it does progress in a chronological manner. You can also see some interesting "themes" running throughout the book: the collapse of the old order, the rise of nationalism, the economic aspect of politics, etc. Definitely helpful as a "crash-course" on the first half of the 20th century, and it perfectly fits within your timeframe!

Of course, these are just a few of the books that I'd recommend for the 20th century, and doubtless there are plenty of others that other AH travelers might (and should!) pop by and recommend too. If however, you would like some further recommendations on books which deal with the First World War, feel free to pm me or drop a follow-up question as well! That might help you out a bit with learning about pre-WW1 incidents. Hope this helps, and happy history reading!

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