I remember having found a crazy way to trick the AI in the original Blitzkrieg game, starting in Fall Weserubung:
1) Play as the Axis. Use your ground troops as usual, this only concerns naval units for now. You start with 3 corps in amphibious transports, and your fleet facing the British fleet. The first (and most random) part is to make your transports get safely past the British Isles and into the Atlantic. To do this either shelter them against the coast and huddle your ships around them, or whatever...can't remember how I did it but you need at least 2 to survive.
2) Send one near Ottawa, keep the other off the US coast near Washington DC.
3) Declare war on the USA. Land near Ottawa and move towards the city. There is no one to defend. The USA will respond by operationally moving their Washington corps into Ottawa.
4) Land on US soil, take Washington. USA surrenders, Washington corps disappears, take Ottawa.
Voila, by the end of 1940 North America is gone

Of course it's completely unrealistic and strategically outrageous, but is was fun to discover. I found out that trick in the demo before I got the full game and haven't tested it since though
