WHY JERUSALEM FELL IN 70 CE?

The fulfilment of Christ's prophecy concerning the destruction of the magnificent temple at Jerusalem ended one phase of God's plan and entered in the next phase -Christ's return to conquer and rule.
During Jesus' time, many Jews were so awe struck and impressed with the grandeur of the Herod's Temple that they replaced the true worship of God with respect and reverence for the Temple complex itself. Jesus was not impressed with the physical structure, because he knew that the Sovereign God is greater than any building that man can construct, no matter how grand and beautiful it is.
Looking back, in 40CE, the Roman senate appointed Herod as the ruler of Judea. He had previously served as the governor of Galilee and was a personal friend of Mark Anthony before Anthony was defeated by Octavian. Later Herod became a friend of Octavian who became the first Roman emperor as Caesar Augustus. Herod ruled Judea for the next 36 years, during which time he began many huge building projects including the building of a new Temple in Jerusalem.
The project was a huge undertaking which required a tremendous amount of labor, money and time. This building was said to be larger and a more beautiful than the one that Solomon built. From the beginning of the Temple project in 19BC, it took 46 years to complete the main building and another 36 years to finish the entire complex. However, 4 years after its complexion, it was totally destroyed and wiped from the face of the earth.
The Romans destroyed the 2nd Temple (Herod's Temple) in 70 CE, on the same date that the Babylonians had destroyed the 1st Temple (Solomon's Temple). 2 Kings 25 says about the first destruction the following, "On the 7th day of the fifth month of the nineteenth year of King Nebuchadnezzar of Babylonia, Nebuzaradan, adviser to the king and commander of his army, entered Jerusalem. He burned down the Temple, the palace, and the houses of all the important people in Jerusalem, and his soldiers tore down the city walls. Then Nebuchadnezzar took away to Babylonia the people who were left in the city, the remaining skilled workers, and those who had deserted to the Babylonians. But he left in Judah some of the poorest people, who owned no property, and put them to work in the vineyards and fields. (2 Kings 25: 8-12)
In the Book of Jeremiah we find how evil thoughts operates in human mind and it repeats its way as it is manifested in the same way through the minds which plot against Jesus. Jeremiah says: "The Lord informed me of the plots that my enemies were making against me. I was like a Trusting Lamb taken out to be killed, and did not know that it was against me that they were planning evil things. They were saying, 'Let's chop down the Tree while it is still healthy; let's kill him so that no one will remember him any more.' Then I prayed, 'Almighty Lord, you are a Just Judge; You test people's thoughts and feelings. I have placed my cause in Your Hands; so let me watch You take revenge on these people." (Jeremiah 11: 18-23)
When Jesus cried out "It is finished," at the same instant, the Herod Temple was torn in 2 from top to bottom. The tombs broke open and the bodies of many holy people who had died were raised to life. The tearing of the curtain of separation from top to bottom forever opened the Way for all humanity to eventually fellowship directly with God the Father.
This is the moment in time that Jesus spoke of to the woman of Samaria when he foretold that the existing worship system would be abolish, and that those who wanted to worship God would no longer need to travel to a specific location to worship: "True worshipers will worship the Father in Spirit and Truth." (John 4:23)
Punishing sinners is always associated with the Law-keeping Covenant observed by God's people. Under Covenant, His people is blessed if they follow His commands and curse if they do not. After  Jesus died on the cross, a New Covenant arose that included Jews and Gentiles. Jesus understood the heart of the vast majority of Jews and their leaders and the fact that they would not repent of their evil ways. This is one of the reasons he wept over Jerusalem as he foretold its destruction.
Hebrews 8 says: "Jesus has been given priestly work which is superior to the one on earth, just as the Covenant which He arranged between God and His people is a better one, because it is based on Promises of better things. If there had been nothing wrong with the First Covenant, there would have been no need for a Second One. But God finds Fault with His people when He says, 'The days are coming, when I will draw up a New Covenant with the people of Israel and with the people of Judah. It will not be like the Covenant that I made with their ancestors on the day I took them by the hand and led them out of Egypt. They were Not Faithful to the Covenant I made with them, and so I paid No Attention to them. Now, this is the Covenant that I will make with My people in the days to come. I will put My Laws in their minds and write them on their hearts. I will be their God and they will be My people." (Hebrews 8: 6-10)
Jesus predicted again the destruction of Jerusalem when he was being led to the place of his execution. The streets along the way were packed with his enemies as well as with those who followed his teachings and were hopeful that he was indeed the prophesied Messiah. Jesus foretold to those showing concern for him and the injustice that was about to befall him, the destruction of Jerusalem and the horrible starvation, sickness, and death that would come upon them before and after the Romans destroyed the city and its Temple.
On 24 August,79 CE, nine years after Roman legionaries destroyed Jerusalem, God sent a powerful eruption in Mount Vesuvius destroying the affluent Roman cities of the Bay of Naples, including Pompeii and Herculaneum, and the temples of Serapis, Isis, Neptune, and Jupiter among others. Also many luxurious public buildings were destroyed by the blast (100,000 times more powerful that Nagasaki / Hiroshima nuclear bombs). The quakes lasted for several days.
In the spring of 80 CE, a fire broke out in Rome, burning large parts of the city for 3 days and 3 nights.
Although the extent of the damage was not as disastrous as during the Great Fire of 64 CE, a great deal of important public buildings were destroyed, including Agrippa's Pantheon, the Temple of Jupiter, the Diribitorium, parts of the Theatre of Pompey, and the Saepta Julia (a building to cast votes) among others. A plague also broke out during the fire. The nature of the disease, however, or the death toll are totally unknown.