What happened in Jerusalem in 70 CE, and why did it change Judaism?

In 70 CE a Roman army under Titus broke into Jerusalem, burned the Second Temple and razed most of the city, ending the main phase of the First Jewish Revolt against Rome. For Jewish history it was a turning point, because the Temple had been the centre of worship and pilgrimage. After it fell, Judaism had to carry on without sacrifices.

The Temple had stood since around 516 BCE (some date it to 450–400 BCE), and under Herod the Temple Mount was doubled in size, becoming the ancient world's largest religious sanctuary. When Titus arrived with at least 48,200 soldiers, the city was crowded with refugees and Passover pilgrims, and rival factions inside were fighting each other and wrecking the food supplies. In the month of Av the Romans captured the Temple Mount and destroyed the Temple. Jews still commemorate the day each year as Tisha B'Av. A year later Titus and Vespasian paraded Temple spoils, including the menorah, in a triumph at Rome.

Most of what we know comes from Josephus, a captured Jewish commander who watched from the Roman side and wrote under Roman patronage, so historians read him carefully. Archaeologists have found piles of fallen Western Wall stones on the street below, which supports the story of destruction.

What came next shaped Judaism ever since. With sacrificial worship gone, Judaism gradually reoriented around Torah study, acts of loving-kindness and synagogue prayer, which culminated in Rabbinic Judaism. Of the major Second Temple sects, only the Pharisees remained, and their survival is attributed to Rabbi Yohanan ben Zakkai, who founded a school at Yavne.