In a general sense, God promised the Jews that if they didn’t obey him, then:
The LORD will drive you and the king you set over you to a nation unknown to you or your fathers … You will become a thing of horror and an object of scorn and ridicule to all the nations where the LORD will drive you … You will have sons and daughters but you will not keep them, because they will go into captivity … The alien who lives among you will rise above you higher and higher, but you will sink lower and lower … He will be the head, but you will be the tail.
All these curses will come upon you. They will pursue you and overtake you until you are destroyed, because you did not obey the LORD your God and observe the commands and decrees he gave you. They will be a sign and a wonder to you and your descendants forever. (Deuteronomy 28:36-46 NIV)
You can read the whole of Deuteronomy 28 for the full gory details. This is what God promised the Jews if they didn’t keep his commands. And they didn’t — and still don’t, generally (though there have always been individual exceptions, of course). Of course, the holocaust also killed many non-Jews (including Christians).
There are claims that some specific Bible prophecies are about the holocaust, but there are multiple other interpretations of these prophecies which are more convincing.