The discovery of the One Ring took Gandalf by surprise, but when it came to the Dark Lord himself, the Wizard was more than prepared for his return. His sole purpose on Middle-earth was to hunt Sauron and stop him from ever rising to power, and Gandalf was better at this than any other wizard in the world. However, there was a key moment before The Lord of the Rings when Gandalf could've weakened Sauron -- but he failed.

To Gandalf's credit, he was an expert when it came to finding the Dark Lord. Most of Middle-earth had grown complacent and believed Sauron would never return, and even the other wizards chose to focus on other activities. But Gandalf was always vigilant, picking up on every lead and making connections all around the kingdoms. But no matter how hard he tried, the laziness of those around him always brought him down.

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Sauron's Return Before The Lord of the Rings

Dol Guldur in Lord of the Rings

Around 1000 years after Sauron lost his One Ring, he began re-establishing himself in Middle-earth as "The Necromancer." He had the isolated fortress of Dol Guldur built by his forces as a secret base of operations, and it was here that Sauron spent centuries regaining his strength. It wasn't until 150 years before The Lord of the Rings when Gandalf finally caught on to the growing rumors and headed straight to Dol Guldur, where his suspicions were finally confirmed -- Sauron had returned.

Such news would seem like a huge cause for concern, yet most of Middle-earth ignored it. Gandalf even rushed back to Rivendell and reported his finding to the White Council, a prestigious group of individuals who watched over Middle-earth. Yet Saruman (the council leader) advised against acting on this information. He persuaded everyone that Sauron was defeated and could never regain his full strength. And in a moment of complete foolishness, everyone agreed with him. In fact, the White Council were so overconfident that they left Sauron alone for 100 years, giving him more than enough time to prepare for war.

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Saruman Allowed Sauron Back Into Middle-earth

If the White Council had taken action right away, then it's likely that Sauron would've been caught off guard and severely weakened once more. In hindsight, it makes sense to strike Sauron early and bulk up Middle-earth's defenses for the impending war, or at the very least warn the other Kingdoms of his presence. It would've saved countless lives in the long run and could've made the Fellowship's journey far easier.

But as for why nothing was done about Sauron's return before The Lord of the Ring, it's mostly down to the Council's trust in Saruman. The White Wizard secretly hoped to use the One Ring for himself and knew that Sauron might be the key to finding it. But this thought never even crossed the Council's mind, for Saruman was sent from the gods themselves to help fight the Dark Lord, so they had complete faith in his word. Plus, what Saruman was saying wasn't completely false, as without the One Ring, there was little Sauron could do but sit and let his minions attack for him.

In the end, everything worked out, and Sauron was destroyed once and for all -- but the White Council couldn't have known that. From the limited information they had, all of them (including Gandalf) made a critical error based on nothing but Saruman's opinion. If they had attacked Sauron, it would've been a tough and (possibly) fatal fight. But Sauron would've been severely weakened and likely far easier to deal with in The Lord of the Ring, and it's all thanks to Saruman and the complacencies of Middle-earth.