The world of Naruto is a realm strife with conflict and war waiting in every corner. This is a fact for one called Naruto Uzumaki, the Jinchuuriki of the nine-tailed fox. Since the day he was born, his life has been filled with misfortune day and night, even as a child.
The ways of the ninja world are not for the faint of heart. Chakra flows through every human and can be used for good or evil, but most use it to enforce their will upon the earth.
Chakra flows through even the Tailed Beasts who can and will destroy the world if given the chance. The protagonist is infused with one and this will cause problems several times in the series. No matter what he does, the brutality of life is upon him.
Disclaimer: The following list are the authors' opinions and contain spoilers.
The ways in which life was cruel to Naruto, including Zabuza and Orochimaru
1) Minato and Kushina's demise
At the beginning of his life, Naruto's parents sacrificed themselves to save the village when they decided to seal Kurama, a Nine-Tailed demon, into their infant son.
This was the first trauma he ever experienced as he lay sobbing while Kurama was being sealed. A painful experience like that is not something that any child should experience.
To trap a demonic entity in a newborn is a plan the couple had to accomplish, even if it was their own son. Their actions have life-long effects on him.
2) Villagers' hatred
The villagers of The Hidden Leaf were abhorrent to the blonde hero when he was a child. They blamed him for killing the fourth Hokage and for being the vessel of the Nine Tails even though Minato's sacrifice saved the village.
Villagers wouldn't allow their children to befriend him and showed resentment for crimes he didn't commit. This only fueled him to yearn for their acceptance.
They cared not for the sacrifice of the late Hokage and treated his son horribly. To them, he was the manifestation of Kurama, not the Hokage's sacred child.
3) Zabuza's cruelty
Zabuza is considered a demon in some aspects, though with his partner Haku they're a menace to society. They're the first true threat to Naruto, who established the series for what it is.
Zabuza almost killed Team 7 in a single blow and even when they managed to escape, he couldn't shake the feeling that he would come for them again. This is one of the many brutal battles he has experienced first hand.
The giant blade he wields has struck down many opponents and no one has survived his blade. It's like his sword has a mind of its own as he slaughters friends and foes alike. No one is safe around him.
4) Orochimaru's shadow
Orochimaru is a constant threat to Konoha and is relentless in his pursuit of immortality. Naruto frequently encounters him at various points in his journey and causes him extreme pain every time.
One fight that comes to mind is when during the Chunnin Exams, Orochimaru defeated him so badly he could hardly move. However, even without encountering him, his influence is everywhere, from Yamato to Sasuke, and even the Third Hokage.
His knowledge stems from the constant experiments and body snatching he has partaken in. The soul he kills is just a drop in the bucket for him. If he continues to live, the world will no longer be safe.
5) Akatsuki's rampage
The Akatsuki are a terrorist group formed under Pain whose sole mission is to collect various Tailed Beasts in order to summon the Ten Tailed Beast. They accomplish this by kidnapping and killing jinchuurikis, then using their Tailed Beast to awaken the Ten Tails.
They've frequently tried to capture Naruto, but to no avail as he has escaped their grasp several times. The fact remains that their insidious presence lingers over him even though he never wanted a Tailed Beast to begin with. This was just one of many ways in which life has been cruel to him.
Their roots seep deep in the world and the blood they spill runs cold.
6) Kurama's rage
As mentioned before, Naruto was infused with the very essence of the Nine Tails at the beginning of his life. Kurama waits in the shadowy jail of his mind, longing for him to break the seal on his imprisonment.
The power of the Nine Tails will have Naruto going mad until someone can subdue him. However, Kurama gets a taste of destructive freedom when he manages to take possession of the boy's body for a short while.
Sometimes he will tempt him with dark promises and almost succeed in escaping his prison, as displayed when Hinata was critically injured during her disastrous battle with Pain. Luckily, Minato's dormant chakra interfered with his plan before Naruto's soul was devoured, but that temptation still lies in his heart, waiting to be consumed.
7) Jiraiya's passing
One of the Sannin and Naruto's mentor, Jiraiya's life was snuffed out by his former student Nagato. He was the guiding light and only father figure to the gutsy ninja in times of need. But when he died, Naruto had no one else to lean on.
Their relationship was silly and lighthearted in some aspects, but Jiraiya was a great protector as well. For example, when Itachi and Kisame arrived at an inn they were staying at, the sage quickly intervened and shielded Naruto from the worst of their attacks.
Jiraiya's legacy casts itself upon the young man as the world marches on.
8) Sasuke's ostracization
Perhaps one of the most negative aspects of life, Naruto's only friend and rival abandoned the Hidden Leaf to seek vengeance with the help of Orochimaru. Naruto tried to convince him to stay, but the Uchiha wanted no part of his old life so they fought in a futile effort to bring him back.
Sasuke was one of the only people who truly understood him as they were both orphaned at a young age and had no one to guide them. This only fueled Naruto's obsession with bringing him home as he considered Sasuke an equal. The cruelty of life shrouded them both.
Sasuke is the dark to his light, and the moon to his sun. They're complete opposites yet their experiences have made them who they are, so his loss is absolutely devastating.
9) The dawn of Madara
When Madara Uchiha was reanimated, it seemed as if the underworld itself awoke from a languid sleep. He broke free of the Jutsu that Kabuto bound him in and unleashed the Eye of the Moon upon the world.
He fought both Naruto and Sasuke, yet they were clearly no match for him in their current state until the Sage of Six Paths intervened. However, even with Sage's guidance, they still had to work together to put a stop to the deplorable Uchiha.
Madara forced the world into slumber as Naruto watched on in horror as his companions were trapped in cocoons and made to experience their own version of false paradise.
By this point, the entire war had taken a toll on him as his chakra reserves were drying up, but Madara would not relent. This was a special form of torment.
10) Kaguya's resurrection
Kaguya was a villain that no one saw coming as she could be described as an alien goddess from the moon. She is the progenitor of the Sharingan and Byakugan and the mother of the Sage of Six Paths. Her powers are so great that she managed to teleport Team 7 to multiple dimensions in the blink of an eye.
Naruto and Sasuke were no match for her until her son bestowed upon them his powers, but even when they attempted to seal her, she froze them in blocks of ice.
A being of mass destruction, Kaguya was the greatest challenge the world had ever faced up to this point. Her presence alone was enough to consume Madara and her powers held him in a death grip.
The cruelty of the ninja world in which Naruto resides cannot be underestimated in any way. Demons and ninjas plagued the land and threatened to destroy him at any minute, but he somehow persevered. Perhaps all of this madness has made him stronger in the end.