* The Izanagi: While Madara was critically wounded, he activated Izanagi, a forbidden jutsu that allows the user to rewrite reality, essentially making any event a "dream" or illusion. Using Izanagi, Madara escaped death.
* The Rinne Rebirth: Madara had a secret plan in place. He'd been manipulating the Akatsuki, a group of rogue shinobi, to collect the nine Tailed Beasts, the powerful creatures that hold immense chakra. Once they were gathered, he planned to use the Rinne Rebirth, a forbidden jutsu that allows the user to bring people back to life.
* The Gedo Statue: He also had a hidden plan involving the Gedo Statue, a massive statue that absorbed the Tailed Beast chakra. This statue was the key to his revival, as it housed the Rinne Sharingan.
* Black Zetsu: He had a mysterious partner, Black Zetsu, a being born from the will of Kaguya Otsutsuki, the progenitor of chakra. Black Zetsu played a key role in manipulating Madara and orchestrating his resurrection.
In short, Madara's "resurrection" was a multi-layered scheme involving:
1. Using Izanagi to escape death during the fight with Hashirama.
2. Manipulating the Akatsuki to gather the Tailed Beasts for the Rinne Rebirth.
3. Using the Gedo Statue to house the Rinne Sharingan.
4. Utilizing Black Zetsu's influence and strategic planning.
It's important to note that while Madara successfully revived himself, he wasn't truly alive. He was a soul inhabiting the Gedo Statue, with a body powered by the Tailed Beasts.