This is a fixed phrase with two forms:
all the world over
the world over (This version is more common.)
It's a literary postmodifier meaning "all over the world; everywhere; throughout the world".
Since it's a fixed phrase with rather unique grammar, we don't really need to analyze it. But if we do so anyway, we might say something like this: The preposition over takes (all) the world as a complement, even though it comes afterwards instead of before. This is unusual, but not unprecedented—it is similar to the preposition ago.
Since the entire phrase is a postmodifier, it follows what it modifies. In this case, that means it modifies the noun jihadists.
It does not mean "in the world that is over there".