OK one example of the weird thing.
Fut envahie => passé antérieur ou voix passive au passé
Conquerront => Futur simple.
For information, in French you can't use the "futur antérieur" to express the past of a present while you use future in the same sentence. Also, when you talk about future in the past, I mean here something that is sure to happen (here the german conquest), you can't use the future
You should have said :
En 1940, la France est envahie , la blitzkrieg est trop forte, ils conquièrent la France
PASSE COMPOSE => PRESENT => PRESENT
or
En 1940, la France fut envahie, la blitzkrieg était (ou fut) trop forte, il conquirent la France
PASSE ANTERIEUR => IMPARFAIT ou PASSE SIMPLE => PASSE SIMPLE
I don't want to play the jerk, two years after the post.