Civilian industry is now separate from the military, which itself splits between dockyards and equipment. Also they have simplified the economy to just 'raw resources'.
Before you needed metal, energy and rare materials but Paradox felt it was an unnecessary burden and instead go for a unified 'raw resources' instead, which feed factories.
"This kind of separation allows us to balance different countries' industrial strengths (the capacity to make ships is not the same as the capacity to make luxuries), and gives the player a more interesting selection of targets for strategic bombing," Paradox, referring to the three-way split of industry.
"Requiring the player to gather several different types of resources in order to manage factories did not necessarily add anything interesting to the mix. Being short on any of them had the same effect no matter what you were lacking (your Industrial Capacity would shrink) and it didn't entirely make sense that you couldn't build things like Militia if you didn't have access to Rare Materials."
"We have simplified the inputs to "Raw materials" which factories use to run. Raw materials act as a limit on your total Industrial Capacity. However that is not the whole Production story. Equipment also has a Strategic Resource cost, without which it takes much longer to produce," they continued.
"Strategic Resources are not accumulated in pools. Instead, they represent the potential flow of resources into your factories. For example if you have 10 Iron you can be building stuff that costs up to 10 Iron at any one time."
Factories will also have an efficiency rating where the longer they produce particular type of equipment they get better at doing so, but changing to something else means they need to retool and build that efficiency back up.
Check out thefor Hearts of Iron IV for more.