Why Aragorn (and His Ancestors) Waited To Claim Gondor's Throne. The first reason that Aragorn hadn't claimed the throne was a matter of semantics. Isildur ruled Arnor, while his brother, Anárion, ruled Gondor. So, technically, Gondor's line of kings didn't run through Isildur.
A descendant of the rulers of Gondor and Arnor, Aragorn is considered the lost heir of Gondor. When he was just two years old, his father was killed by Orcs and his mother sent him to live among the Elves in Rivendell. He was raised by Elrond, the half-Elf Lord of Rivendell, and renamed Estel.
So why was Aragorn's claim accepted in Gondor when Arvedui's had been rejected? Part of the reason is of course that Aragorn was the one coming to the throne as a victorious general who had helped save Gondor from disaster, giving him that in common with the successful claimant Eärnil.
He feels unworthy of the throne because the same blood runs in his veins that ran in Isildurs, and Isildur was too weak to resist the power of the ring after he cut it from Sauron's finger in the Battle of the Last Alliance.
"He was Aragorn son of Arathorn, the nine and thirtieth heir in the right line from Isildur, and yet more like Elendil than any before him." Aragorn was a descendant of Elros Tar-Minyatur.
Why did Aragorn wait so long to become King of Gondor?
Why is Aragorn called Isildur's heir?
After the war ended Elendil was dead. Therefore Isildur, his eldest son, was then the (last) rightful king of both Gondor and Arnor, and therefore his descendant Aragorn was also the rightful king of both kingdoms.
Arvedui, Isildur's Heir through twenty-three generations, was the last King to rule in the north; he attempted to reclaim the High Kingship, but failed, and the last remnant of royal Arnor was overrun by its enemies. Now the line of Isildur in the north became forgotten by nearly all.
Éowyn falls in love with Aragorn, but though he respects her, he does not return her feelings, as he is betrothed to the elf Arwen. As Aragorn points out, her duty is with her people; she has to shoulder the responsibility of ruling Rohan in Théoden's stead when the war-host of Rohan go to war.
In The Lord of the Rings: Return of the King, Éowyn asks Aragorn his age and is shocked to learn that he is actually 87 despite looking no older than 40. But it is revealed that Aragorn is one of the Dúnedain—a descendant of Númenor—blessed with long life.
Eärnur was the thirty-third and last King of Gondor until the accession of Aragorn II Elessar. He took the throne upon the death of his father Eärnil II in TA 2043, and after his disappearance the Stewards of Gondor ruled in his name for many generations.
Heir of Isildur was the title of thirty-nine lords of the Dúnedain descended in right line from Isildur the son of Elendil, from his son Valandil to Aragorn Elessar, who reunited the Kingdoms of the Dúnedain in Middle-earth.
Due to dissention among the sons of King Eärendur, the realm of Arnor was divided in three separate kingdoms. The eldest son, Amlaith, became the first King of Arthedain and his descendants maintained the line of Isildur while the line died out in the other two kingdoms.
Elrond didn't want his daughter to die. Her choosing to marry Aragorn meant she chose to die, not to sail into the west with her people. His qualms with Aragorn were more about Arwen's mortality than anything else.
He died at the age of 210, after 122 years as king. The graves of the hobbits Merry and Pippin (who had died in Gondor 58 years earlier) were set beside his. He was succeeded on the throne by his son, Eldarion. Arwen, heartbroken by the loss of her husband, died shortly afterwards in Lothlórien.
The Lord of the Rings films showed Arwen (Liv Tyler) dying due to her connection to the One Ring. The closer Frodo Baggins (Elijah Wood) and Samwise Gamgee (Sean Astin) get to Mount Doom, the closer she gets to death.
So the simple explanation is that Denethor saw Aragorn as a threat to him; he was the ruler of Gondor, and if Aragorn appeared as the heir of Elendil, he would be acclaimed as king.
They set the boat adrift in the river toward the Falls of Rauros, singing the "Lament of the Winds" as his funeral song. Three days later, Faramir, to his and their father's great grief, saw the boat bearing his dead brother floating down the River.
When Aragorn leads his company away from Edoras towards the Dwimorberg, the haunted mountain, and the Paths of the Dead, he leaves Éowyn behind him, his last words to her nothing more than, “Nay, lady”.
Sauron uses the Palantír to show Aragorn a dying Arwen (a scene from the future) in the hope of weakening his resolve. The films portray Arwen as becoming human through her love for Aragorn; as in the novel, she follows the choice of her ancestor Lúthien to become a mortal woman for the love of a mortal man.
Her constitution already weakened by loneliness and despair, combined with physical injuries, Éowyn then succumbed to the Black Breath. Théoden, not knowing that she was nearby, told Merry with his dying words that she had been "dearer than daughter" to him.
After he was attacked by the orcs, they transported his lifeless body to Mordor at Sauron's behest. Sauron revived Isildur with one of the nine rings, and then tortured him until his spirit was broken and he became a Nazgûl.
Isildur felt that he was entitled to it. He also didn't fully realize how dangerous it was. Finally, Tolkien wrote in his letters that nobody had the strength of will to destroy it, there in Mount Doom where its power was strongest.
Aragorn was a descendant of Elros Tar-Minyatur through the line of the Lords of Andúnië to Elendil, High King of Arnor and Gondor. Like all of the kings before him, he was related to Elrond through the House of Elros.
