Question:If God promised the land to Abraham, then how come God let it be destroyed and taken over by the Assyrians and Babylonians?
God made other promises to Israel that He also fulfilled. God promised to destroy Israel when it disobeyed.
"And after all this, if you do not obey Me, but walk contrary to Me, then I also will walk contrary to you in fury; and I, even I, will chastise you seven times for your sins. You shall eat the flesh of your sons, and you shall eat the flesh of your daughters. I will destroy your high places, cut down your incense altars, and cast your carcasses on the lifeless forms of your idols; and My soul shall abhor you. I will lay your cities waste and bring your sanctuaries to desolation, and I will not smell the fragrance of your sweet aromas. I will bring the land to desolation, and your enemies who dwell in it shall be astonished at it. I will scatter you among the nations and draw out a sword after you; your land shall be desolate and your cities waste. Then the land shall enjoy its sabbaths as long as it lies desolate and you are in your enemies' land; then the land shall rest and enjoy its sabbaths. As long as it lies desolate it shall rest-for the time it did not rest on your sabbaths when you dwelt in it. 'And as for those of you who are left, I will send faintness into their hearts in the lands of their enemies; the sound of a shaken leaf shall cause them to flee; they shall flee as though fleeing from a sword, and they shall fall when no one pursues. They shall stumble over one another, as it were before a sword, when no one pursues; and you shall have no power to stand before your enemies. You shall perish among the nations, and the land of your enemies shall eat you up. And those of you who are left shall waste away in their iniquity in your enemies' lands; also in their fathers' iniquities, which are with them, they shall waste away" (Leviticus 26:27-39).
They would be driven from the land.
"When you beget children and grandchildren and have grown old in the land, and act corruptly and make a carved image in the form of anything, and do evil in the sight of the LORD your God to provoke Him to anger, I call heaven and earth to witness against you this day, that you will soon utterly perish from the land which you cross over the Jordan to possess; you will not prolong your days in it, but will be utterly destroyed. And the LORD will scatter you among the peoples, and you will be left few in number among the nations where the LORD will drive you. And there you will serve gods, the work of men's hands, wood and stone, which neither see nor hear nor eat nor smell" (Deuteronomy 4:25-28).
They would cease to be a nation.
"Then it shall be, if you by any means forget the LORD your God, and follow other gods, and serve them and worship them, I testify against you this day that you shall surely perish. As the nations which the LORD destroys before you, so you shall perish, because you would not be obedient to the voice of the LORD your God" (Deuteronomy 8:19-20).
All these things happened as God stated. Israel sinned grievously against God, despite God’s longsuffering. The northern tribes were removed from the land.
"For so it was that the children of Israel had sinned against the LORD their God, who had brought them up out of the land of Egypt, from under the hand of Pharaoh king of Egypt; and they had feared other gods, and had walked in the statutes of the nations whom the LORD had cast out from before the children of Israel, and of the kings of Israel, which they had made. Also the children of Israel secretly did against the LORD their God things that were not right, and they built for themselves high places in all their cities, from watchtower to fortified city. They set up for themselves sacred pillars and wooden images on every high hill and under every green tree. There they burned incense on all the high places, like the nations whom the LORD had carried away before them; and they did wicked things to provoke the LORD to anger, for they served idols, of which the LORD had said to them, "You shall not do this thing." Yet the LORD testified against Israel and against Judah, by all of His prophets, every seer, saying, "Turn from your evil ways, and keep My commandments and My statutes, according to all the law which I commanded your fathers, and which I sent to you by My servants the prophets." Nevertheless they would not hear, but stiffened their necks, like the necks of their fathers, who did not believe in the LORD their God. And they rejected His statutes and His covenant that He had made with their fathers, and His testimonies which He had testified against them; they followed idols, became idolaters, and went after the nations who were all around them, concerning whom the LORD had charged them that they should not do like them. So they left all the commandments of the LORD their God, made for themselves a molded image and two calves, made a wooden image and worshiped all the host of heaven, and served Baal. And they caused their sons and daughters to pass through the fire, practiced witchcraft and soothsaying, and sold themselves to do evil in the sight of the LORD, to provoke Him to anger. Therefore the LORD was very angry with Israel, and removed them from His sight; there was none left but the tribe of Judah alone" (II Kings 17:7-18).
When the remaining tribe also sinned, it too was removed.
"Nevertheless the LORD did not turn from the fierceness of His great wrath, with which His anger was aroused against Judah, because of all the provocations with which Manasseh had provoked Him. And the LORD said, "I will also remove Judah from My sight, as I have removed Israel, and will cast off this city Jerusalem which I have chosen, and the house of which I said, 'My name shall be there'" (II Kings 23:26-27).
Yet, God in his mercy promised that the second captivity would only last 70 years. The whole nation would not be restored, but a remnant would return to the land (Jeremiah 25:8-13; Isaiah 10:20-23). Thus, the promise to Abraham continued. This was fulfilled as Ezra, Zerubbabel, and Nehemiah returned the people to Israel.
Like a broken jar, Israel was repaired, but it was never whole like it once was.
"And I will make void the counsel of Judah and Jerusalem in this place, and I will cause them to fall by the sword before their enemies and by the hands of those who seek their lives; their corpses I will give as meat for the birds of the heaven and for the beasts of the earth. I will make this city desolate and a hissing; everyone who passes by it will be astonished and hiss because of all its plagues. And I will cause them to eat the flesh of their sons and the flesh of their daughters, and everyone shall eat the flesh of his friend in the siege and in the desperation with which their enemies and those who seek their lives shall drive them to despair. Then you shall break the flask in the sight of the men who go with you, and say to them, 'Thus says the LORD of hosts: "Even so I will break this people and this city, as one breaks a potter's vessel, which cannot be made whole again; and they shall bury them in Tophet till there is no place to bury. Thus I will do to this place," says the LORD, "and to its inhabitants, and make this city like Tophet. And the houses of Jerusalem and the houses of the kings of Judah shall be defiled like the place of Tophet, because of all the houses on whose roofs they have burned incense to all the host of heaven, and poured out drink offerings to other gods."'" (Jeremiah 19:7-13).
God kept all his promises.