The form of Judaism that emerged after the Roman destruction of the Second Temple in 70 CE — replacing Temple sacrifice with prayer, priestly authority with rabbinic scholarship, and territorial religion with a portable legal and intellectual system that could survive anywhere on earth.
When the Romans destroyed the Temple in Jerusalem in 70 CE, they thought they were destroying Judaism. What they actually destroyed was one form of Judaism — the Temple-based, sacrificial, priestly religion of ancient Israel. What emerged from the ruins was something entirely new: a religion organized around a book rather than a building, around scholars rather than priests, and around law rather than sacrifice. That religion is what most people mean when they say 'Judaism' today. It was invented in catastrophe and has outlasted every civilization that tried to destroy it.