‘were it not for’ + noun phrase expresses that someone or something prevented something from happening. For example:
Were it not for the cataclysmic events which overtook them,
it’s entirely possible that raptors, rather than humans,
would have become the dominant species on this planet.
C2 point 132 in CLAUSES/conditional is defined as:
‘Were it not for’ + noun phrase to introduce conditions in formal contexts.
*The big corpora do not allow for much detail to be discovered about this string. But looking through random examples suggests this structure is often used to discuss Darwinian evolution: