The Roman Emperor Vespasian ordered the destruction of Jerusalem's Temple in A.D. 70., to punish the Jews for what became known as the First Jewish Revolt. This Roman coin from A.D. 71, issued by Vespasian, commemorates his capture of Judea, the province represented iconographically by the mourning woman to the right. The date palm represents the agricultural produce and lands he captured.
The Roman Reaction ...
Firstly their immediate reaction. For Titus Judaea was literally a Triumph, and scenes from it are depicted on his Arch in the Forum, one of which depicts Treasure from the Temple being carried as part of it.
This panel is important in terms of the history of the Temple Treasures after AD 70, which I will discuss in the future, but first I'd like the point out the evidence for several other Triumphal Arches erected to celebrate this campaign.
A second Arch of Titus is known to have stood at the Circus Maximus. Fragments of the hyperbolic inscription survive (CIL 6.944 = ILS 264):
The Senate and People of Rome dedicate this arch to the Emperor Titus … because, with the Senate's advice and counsel and with the auguries, he conquered the nation of the Jews and destroyed Jerusalem, which all of the generals, kings, and nations before Titus had either failed to do or even to attempt.This second Roman arch can be located on the Forma Urbis Romae (here); the Severan the marble plan was displayed in the Templum Pacis, which the Flavians erected to display the booty from the Temple in a continuation of the celebration of their Judean triumph.
here). The text is highly fragmentary, but the key word is "arch" and the name Flavius Silva, governor of Judaea and conqueror of mighty Masada, confirming that it belonged to an arch commemorating this campaign and not Hadrian's. This is the first proof we have of a Roman monument on the Mount immediately after 70 rather than from the time of Hadrian. A tentative reconstruction of the text reads: : "OS E // V L FLAVI A // M ARCUM DE F // IO ATHENAG // MAXIMO" (source).
The final Arch was in Antioch and comes from the same section of Malalas (1986 translation by E.Jeffreys, M.Jeffreys and M.Scott, et al) in which he discussed the theatre built by Titus from the spoils of the campaign:
The structure was almost certainly in the form of an Arch, and the fact that Vespasian ordered it to be decorated with the bronze Cherubim they had taken from the Temple, and four bronze bulls taken from Jerusalem, confirms its triumphal nature.
But what about Jews and earliest Christians ...
The Destruction of the Temple in turn accelerated the diaspora, for if Jews no longer had a Temple in which to offer sacrifices and pray in Jerusalem, there was less reason for them to stay there. It's interesting to read how the Romans saw the Jews and Christians, and how early sources conflate the two.
Both were actively trying to convert in first century Rome, and both Jews and Christians for example claim Flavia Domitilla as their convert. Cassius Dio says that Domitian had her, his own niece, and her husband the consul Titus Flavius Clemens charged with atheism [Epitome of Cassius Dio, 67.4] because they had "drifted into Jewish ways" - ie become monotheists. Clemens was executed in AD 95, a charge normally reserved for treason, and the treason her was presumably failure to sacrifice to the Imperial cult; Domitilla was exiled. Suetonius [Domitianus 15] does not mention Clemens' religion, saying he was executed "suddenly and on a very slight suspicion" but continues on to Domitian's own death at the hand of Domitilla's steward Stephanus. Although Clemens was revered by later Christians as a martyr, and Domitilla as a saint, I give greater weight to the Jewish tradition, since we have much better attested contact between Jews and the Imperial family. Domitilla's uncle had a long relationship with Julia Berenice, and before that Poppea Sabina had intervened as a phil-Semite on behalf of Berenice and her brother Herod Agrippa II.
It's still unclear how they two groups saw each other, and how they interrelated at the time, or when they diverged, but after the Destruction of the Temple is a logical point for this to have accelerated.
In the early first century AD Judaism was a proselytizing religion, and attracted a large number of followers. The main reason it did not close the deal with more converts was that the rabbis were intransigent about one issue: circumcision. Men were reluctant to give up a piece of themselves, and many pagans remained 'God fearers' but did not become full Jews.
Early Christianity under Paul was more flexible. At the Council of Jerusalem (ca. AD 70; although presumably not whilst Titus was besieging the city), the followers of Jesus re-stated that most of the laws of Moses were to be kept - such as the requirement to keep kosher. There were two major departures from Jewish law, which would in effect change the course of history. The first was waving the circumcision requirement, which immediately let to a flood of converts. The second was discussing the concept that Jesus was Christos - the Messiah. The Messianic nature of Jesus was not however affirmed as universal orthodoxy until the Council of Nicaea (AD 325).
This split between the Jews and the followers of Jesus soon after the fall of Jerusalem would in due course change history.