Hearts of Iron II: Doomsday Hints for PC
For this you must start a game and save your game.Then quit the game and where the menu is there where you can load games instead of clicking on the country you selected
Click on a different country.
Now whatever you do with this country save the file on your previusly made file and when you select your old country the changes are there .Eg You selected Germany for the first and you saved and then started with an another country.
Whatever you did with germany will stay and now as France you can open the trade meneu and trade with Germany 100 oil,100 metal,100 energy etc after you save and start with with germany again you will find that the Trade aggrement is still there.