Germany believed that by mid 1942 the Soviet Union would be to strong to attack so it had to be 1941 ! The Soviet Union was building up its armed forces ! The Soviet Union was hopping for a long hard war between Germany and Britain / France. The Soviet Union was plaining to attack Germany after she weakend herself against the western allies. But there was no weakening ! British aircraft production jummped ahead of Germany's in 1939 and Germany could never cetch up. Germany's only chance to invade Britain was 1940 !
{Note: Germany did build more aircraft than Britain did in 1944 but it was far less in total millions of tons of aircraft built (4 Engine Bombers). Britian like America decided in mid 1943 not to expaned there aircraft production to there full potential ( 50 thousand aircraft per year Britian and 150 thousand aircaft per year America) because it no longer was needed and this production capabuility could be used for other war machines.
There are 2 ways to show the start of WWII in a game, script the rules to start when the war did or use the political what if's. The best I beleive is have both. Script the game to kick off during historical time lines then have optional rules for the political what if's. This will then keep all happy !
Joe