Once I played in Vicky multyplayer with my friend.
I played as USA. He did as Russia. Helgi (this is my friend) made a roller walk along Germany, took over 600 points of badboy and sent his troops to France. He didn't have any fleet, so he couldn't defeat Brazil. I helped him and landed my troops there, but my fleet was destroyed. After the war ended I wasn't able to return my troops home.
SO, THIS IS THE WAY WHY I'VE CONQUERED BOLIVIA.
The conclusion: unoccupied army of Americans will always find oil.