In Rebirth of Evangelion, the first movie is almost a fidedign retelling of the original anime series. But soon it begins to deviate more and more (and more `/sad`...), until I really wasn't sure of what I was watching anymore (but I digress).

So, lets consider both storylines as happening on **parallel universes**. 

What is the event (onscreen or not) in the Rebirth series that is the turning point of the forking/deviating storylines?

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While this may seem opinion-based, it is not. I am asking you to compare the rebirth movies to the original series, script or storyline-wise, and backtrack the visible differences to their sources, pointing to a specific event that happened onscreen or was mentioned that may be the cause of those differences, looking backwards for the cause of that other event. Pepper your answer with references, please.

You may add a few speculations in making your chain of causality, if the events have a significant impact or relation.