I don't recall where I read this, but a historian argued that if the Jewish population had grown at the same rate from ancient times to now as various other populations, it would be something like 200 million today. Besides the various attempts at genocide, there probably was a good deal of assimilation into the majority cultures they lived in over the centuries. If you can find a way to have the Jewish nation not be quite so scattered so that it can form a large minority - or majority - in a few nations, its population can grow much more than it did.