Hearts of Iron IV has just received its latest piece of DLC - Battle of the Bosporus. This is a smaller 'Country Pack' that only adds new narrative content for Turkey, Bulgaria, and Greece, so it's distinct from the more impactful La Résistance expansion that was released back in February.
These three nations are all getting new 'Focus Trees', a narrative-driven mechanic that all nations have that lets you progress down a set path, one step at a time. Some act as shortcuts for various game elements, others either grant buffs (or remove existing debuffs) and in later years these trees have been used as a guideline for steering your nation down one of the handful of political routes available in the game.
They are in equal parts a creative and disruptive force within the WW2 grand strategy game, especially in more recent add-ons where they've been used to enhance the sandbox nature of the core design. Entire sections of the game, like diplomacy and production, are rendered meaningless because you can get all you need and more by just progressing down the right path of the focus tree.
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Hearts of Iron 4's next country pack features Greece, Bulgaria, and Turkey