The Great Diaspora
In AD 70, Roman legions under the command of Emperor Titus utterly destroyed much of Jerusalem, including the magnificent Temple of Herod the Great. (Herod's Temple is prominently featured in all four Gospel accounts in the Bible. For example, that's where Jesus overturned the money-lenders' tables.) The destruction of Jerusalem was the Roman Empire's means of payback for the Jewish rebellion that had been simmering in the city for years.
From this incident, we clearly understand the Romans were not subtly-nuanced diplomats, masters of the proportional response. (Spray paint the walls of the city with graffiti? Rome doesn't just remove the graffiti, nor just the walls—Rome goes ahead and removes the city too. You know, just to be sure.)
The surviving Jews of Jerusalem (and the surrounding countryside of Judea) mostly scattered to the east and north, and eventually their descendants emigrated into Europe and many parts of Asia. This dispersion of the Jews out from their homeland is called the Great Diaspora.
The Great Diaspora created a problem for end-times Bible prophesy, though. The prophetic books of Daniel and the Revelation of John, in particular, speak extensively about end-times events that occur in a Jerusalem populated by Jews, and with a fully-operational Temple in place. In fact, you can't really bring the Antichrist onto the scene until you've got Jews in Jerusalem at war with their numerous adversaries. According to Daniel 9:27, for example, the Antichrist gets all the hostile nations to sign a peace treaty with Israel and later betrays the Jews by desecrating their Temple.
The Great Diaspora officially ended though, when the Jewish State of Israel was created by decree on May 14, 1948. Today there are millions of Jews living in Israel and Jerusalem. They are surrounded on all sides by adversaries. The stage is finally reset for the end-times events described in the Bible.