I guess one way to go about it would be to try and decompose the entire paragraph into testable fragments:

    1. Just before WW2 the Haber Bosch process ... was invented
    2. for fixing atmospheric nitrogen into fertilizers/explosives 
    3. (same thing basically). 
    4. Shortly after the war it was widespread,
    5. and since then there was no starvation in any developed or even semi-developed country.
    6. Hitler started WW2
    7. to annex Ukraine 
    8. because of its fertile soil.
    9. Basically he wanted colonies 
    10. without the inconvenience of dealing with the sea.
    11. Like soviets and Americans had.
    12. Shortly after WW2 
    13. it ceased to make sense to invade for farming land.
    14. It's not the only factor (nukes are another), but it is a very significant factor. 

You could probably decompose it further (so like, 'farming land' could be a fact, because you can farm on land). My feeling is it's quite hard to make a rigorous distinction between factual statements and statements in general - there's just an awful lot of factual content in language as commonly used, and some of it seems to have crept into this comment.