Hearts of Iron IV's latest expansion, No Step Back, is out right now and this could easily be one of the WW2 war game's definitive releases. Which is a bit excessive if you ask me, because HOI4 is already Paradox's most popular grand strategy game.
The expansion itself largely focuses on Focus Tree updates for the Soviet Union, Poland, and the Baltic nations of Lithuania, Latvia, and Estonia. There are also extra features that build on top of new free aspects, such as individual supply mechanics that build on top of the free logistics overhaul, and a tank designer similar to the ship designer included in the Man the Guns expansion.
From what we've played so far, not only are the new mechanics fun, but the WW2 game seems to run more smoothly as well thanks to a bunch of behind-the-scenes updates. We'll need to wait and see what this does to the war game's meta, and you may need help re-learning how everything works. Speaking of help, a bunch of brand-new tutorial videos have now been introduced for individual mechanics that you can watch in-game to bring yourself up to speed.
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A million people played Hearts of Iron 4 in November, declaring 400,087,356 wars