Originally Posted by huzzah
Well they will have to because the average movie going audience will end up confused just as I am right now.
In the comics the Sentinels were already the threat even before the DOFP series.
In the film verse they dont exist. So why send someone back to the past to stop a threat that's never existed? Even if you send someone back to the past, just before the point of creation of the Sentinels, then in the future the threat doesn't exist. Therefore there was never a need to send someone back to the past in the first place.
They might show that Sentinels did exist in some secret base but hadn't yet been unleashed.
Or it might be some event that leads to Sentinels being built.
In the animated series, the Sentinels had already been built at the time of the assassination.