THE ORIGEN OF THE NEPHILIM.

According to the Scripture, the Nephilim were the offspring of the "sons of GOD" and the "daughters of men" before the Flood.
The Nephilim later inhabited Canaan at the time of the Israelite conquest of Canaan, and were known as 'Amorite', descendants from the Hamitic race. (Genesis 10; 1 Chronicle 1)
In Abraham's Time the King of Elam in coalition with 3 other kings raided to the SOUTH of Canaan and defeated some of the Amorites dwelling at Hazazon-Tamar, SOUTH WEST of the DEAD SEA.
Three Amorite Men living in Hebron were then confederates of Abraham and as such aided Abraham in pursuing and defeating the invading Kings, thereby rescuing his nephew Lot. (Genesis 14)
Sometime after GOD advised Abraham that when 'the error of the Amorites had finally come to completion,' Abraham's descendants would return to Canaan from an alien Land and would take possession of the Amorite's Land. (Genesis 15)
Still, shortly before Jacob's death in Egypt, he promised Joseph: "I do give you one shoulder of Land more than your brothers, which I took from the hand of the Amorite by my sword and by my bow." (Genesis 48) When he promised Joseph, Jacob's prophetic words envisioned the future conquest of Canaan by FAITH as though it were already effected, with Jacob taking the Land of the Amorite by LAW.
In Deuteronomy 3 we find a description of power that the sons of the Amorite had through the person of King Og, popularized as the King's Road to rule the World.
"We moved NORTH toward the REGION of BASHAN, and King Og came out with all his men to fight us near the Town of Edrei. But the LORD said to me (Moses), 'Do not be afraid of King Og, I am going to give him, his men, and all his territory to you. Do the same thing to him that you did to the Amorite king Sihon, who ruled in Hesbon." (3:1-2)
"At that Time we took from those 2 Amorite Kings (Sihon and Og) the Land EAST of the Jordan River, from the Arnon River to Mount Hermon. (Mount Hermon is called Sirion by the Sidonians, and Senir by the Amorites)" (3: 8-9)
"We took all the territory of King Og of Bashan: the Cities on the Plateau, the Regions of Gilead and of Bashan, as far EAST as the Towns of Salecah and Edrei. (King Og was the last of the REPHAIM. His coffin, made of stone, was 6 feet wide and almost 14 feet long according to standard measurements. It can be still be seen in the Amorite city of Rabah)" (3: 10-11)
In Numbers 21, GOD received the vow that the Israelites did concerning the Nephilim.
"When the Canaanite king of Arad in the SOUTHERN part of Canaan heard that the Israelites were coming by Way of Atharim, he attacked them and captured some of them. Then the Israelites made a VOW to the LORD: "If YOU will let us conquer 'these people (the Nephilim)', we will unconditionally dedicate them (their power) and their cities to YOU and will destroy them. The LORD heard them and helped them to conquer the Canaanites. So the Israelites completely destroyed them and their cities, and named the place Hormah.
Ezekiel the prophet, who lived in exile in Babylon during the period before and after the Fall of Jerusalem, addressed these distinctive character of people, who were Amorite (Nephilim) in spirit, in a vivid and symbolic way, by saying:
In the 12 Year, in the 12 Month,  on the 1st Day of the month, the WORD of the LORD came to me:
"Son of a Man, raise a lamentation over Pharaoh king of Egypt, and say to him: 'You consider yourself a Lion among the Nations, but you are like a Dragon in the Seas; you burst forth in your Rivers, trouble the Waters with your feet, and foul their Rivers.' " (32: 1-2)
Thus says the LORD GOD: "I will throw MY NET over you with a host of many peoples;  and I will haul you up in MY DRAGNET. And I will CAST you ON the GROUND, on the OPEN FIELD I will FLING you, and will CAUSE all the BIRDS of the AIR to SETTLE on you, and I will GORGE the BEASTS of the whole EARTH with you. I will STREW your FLESH upon the Mountains, and fill the Valleys with your CARCASS. I will DRENCH the Land even to the Mountains with your flowing BLOOD; and the WATERCOURSES will be FILL of you. When I BLOT you out, I will COVER the HEAVENS, and make their STARS DARK; I will COVER the SUN with a CLOUD, and the MOON shall NOT give its LIGHT. All the BRIGHT LIGHTS of HEAVEN will I make DARK over you, and put DARKNESS upon your Land." (32: 3-8)
"I will trouble the HEARTS of many peoples, when I carry you CAPTIVE among the Nations, into the countries which you have not known. I will make many peoples APPALLED at you, and their kings shall shudder because of you, when I brandish MY SWORD before them; they shall tremble every moment, every one for his own life, on the DAY of your DOWNFALL." (32: 9-10)