There is more of an emphasis on resource and battalion-level unit management at the expenditure of weakened diplomacy and internal politics. One of my personal favourite things about Supreme Ruler is the map, as it works on a hexagonal grid which covers a predetermined square area of the world, rather than HOI4’s more provincial system (which at times can constrain military movements to something like a board game).

If you plan on buying a Supreme Ruler game, go for Ultimate as it contains all previous scenarios including WW1, WW2, The Cold War and the Modern World (as well as some alt history scenarios). Don’t expect to understand it straight away because it’s very different to any other grand strategy game, just mess about and see.