I may be over-complicating this. And possibly this idea may not be that good to implement for the new comer. Also, I searched some but did not find an idea similar to this. But if this is a replica of someone's previous, I apologize.
I'd like to see roughly six new units added to the game and a new dynamic. Trade and resource transfer.
1st Example: Instead of having ore 'in country' where it's available to all factories/workshops at once... to manage the placement of resources in cities. This may or may not include an additional building to make and maintain (warehouses) for storing materials. In order to build items, the materials need to be present in the same province/city. Money can be exempt from moving from province to province.
2nd Example: You have a warehouse built in a city and two of the necessary resources and money to build a tank (iron, wood, and money) but you lack several hundred tons of oil in this province. In two provinces away you have stored excess oil. So, you'll have to transport that oil from there to your current province.
For this you need one building with 2 levels. A warehouse and a market warehouse. The first being used simply to store materials in a province and able to send and receive within the country. The 2nd level would be a point from which to send and receive materials to other countries.... skip down to read more on this.
Transportation of materials. This is where three new units would be necessary:
Truck
Train
Cargo Ship
Attributes of these three new units would be something like this:
Truck-
Strength on Land - .4
Strength on Sea - Null (or .2)
Speed on Land - 80 km/h
Speed on Water - Null (or 15 km/h)
Tons of material they can haul - 100 tons
Material cost to build-
Build Time .5 days
$2000
500 iron
1000 oil
Train-
Can only run on enable track in province
Strength on Land - .6
Strength on Sea - Null (or .2)
Speed on Land - 110 km/h
Speed on Water - Null (or 10 km/h)
Tons of material they can haul 1500 tons
Material cost to build-
Build Time - 1 days
$6000
1000 iron
2000 oil
Cargo Ship-
Strength on Land - Null (or .2)
Strength on Sea - .5
Speed on Land - Null (or 10 km/h)
Speed on Sea - 70 km/h
Tons of material they can haul - 4000 tons
Speed on Water 40 km/h
Material cost to build-
Build Time - 1.5 days
$6000
1000 iron
2000 oil
Production of these units would be something like-
Workshop 1 for trucks.
Workshop 2 for trains and can only run on tracks.
Harbour for cargo ships.
Stock Market and material transfers-
Currently I've noticed these are relatively instantaneous. You buy wood and it's automatically there and available to use for building.
With this extra concept in place... placing materials for sale on a market would mean you need ways of transporting those goods. This would allow for trade routes to be enabled.
Example: if you are in the US and a trade is initiated with someone in east europe via the market (you place a sell and they accept it) there would be a function to begin transfer of those materials starting from your closest market and routes to the eastern europe country would have to be open or subject to attack in hostile countries. Upon receipt of the goods, payment is transferred to the shipping country. If materials are destroyed en route... then no transaction occurs.
Politics involving trade units-
If a unit transferring material from one country to another across your borders, you can have the option to allow that or not. By default it should allow transport units through your territory as they can't attack. The kicker should be- if you do attack transport units there should be a penalty or you go to war with their owning country. Thus there is a fallout to blockading countries and those that trade with them.
Open to suggestions. I know this would involve quite a bit of work, but may be very beneficial.