Rivalries in Naruto can be sparked over something as momentous as differing philosophies on how to run the world or something as simple as two people fighting over a crush.
The same could be said of any rivalry, really, but the truth is that several of these rivalries have proven fatal for the Hidden Leaf Village/Konoha. From friendships being torn apart to immense levels of destruction and lives lost, quite a few have resulted in pain and devastation.
On the other hand, several have benefited either the people involved or the village as a whole.
Note: This is only the author's opinion and contains spoilers for all of Naruto and Boruto up to its current chapter.
Five rivalries in Naruto that left Konoha devastated
1) First Hokage vs Madara
Konoha was nearly wiped out by Madara Uchiha before it even started! As detailed late in Naruto Shippuden, Harashima Senju (the First Hokage) and Madara Uchiha collaborated to end the bitter Senju/Uchiha rivalry after the Warring States period. The founding of Konoha was to be a significant bridge to peace between these two clans.
While the village was founded on peaceful principles, sadly, Madara and Harashima disagreed on where things should go from there.
The former feared that the Senju would exploit and oppress the Uchiha, so he gathered followers to overthrow the First Hokage. After several devastating battles, including one that created the Valley of the End, Madara was assumed dead.
The Uchiha's treatment was a self-fulfilling prophecy that led to the next entry.
2) Danzo vs Third Hokage
This rivalry proved most fatal, mainly to Danzo's insurmountable and detestable ego. While the Third Hokage, Hiruzen Sarutobi, was a kind and emphatic ruler who always tried to look after everyone in Konoha, Danzo was his exact opposite.
Tensions and clashes between the two never sparked into open conflict, but a lack of oversight into Danzo's operations led to untold bloodshed.
From the start, Danzo considered himself Konoha's ultimate protector and that only his particular brand of justice counted. He formed Root and used them to assassinate people.
Danzo also created tension with the Uchiha by advocating they be blamed for the Nine-Tailed Fox attack and not allowed to participate in the defense. All this led to the Uchiha Clan massacre, Orochimaru's experiments that left many dead, and Danzo's death down the road.
3) Jiraiya vs Orochimaru
A darker reflection of the Naruto vs Sasuke rivalry, Jiraiya and Orochimaru are former teammates, and the former had always considered Orochimaru to be a close friend.
Much like Naruto, Jiraya worked hard to compete with Orochimaru considering how strong he was. Even though their paths diverged after becoming the Legendary Sannin, Jiraiya always tried to stay in touch.
When Orochimaru eventually defected from Konoha, Jiraiya tried harder than anything to get him to return but failed. He ultimately rejected Hokage's position for his failure, and Orochimaru would return to Konoha years later to burn it down.
This ultimately resulted in a massive loss of life, from Orochimaru's twisted experiments to the Third Hokage's death.
4) The Uchiha Clan vs The Senju Clan
This one goes back to the ancient times of Indra vs Asura, but for the sake of simplicity, we're only focusing on the Uchiha Clan's bearing of Indra's curse. The curse of hatred basically states that the more people hate, the stronger they become.
The Uchiha Clan hated the Senju long before the massacre occurred, as they were the two most powerful clans during the Warring States Era.
The politics of isolation and fear of the Uchiha Clan made Madara's fears self-fulfilling since the Konoha Council disallowed any Uchiha from defending against Kurama's attack. Hence, the Uchiha were increasingly isolated in the village out of fear of reprisals.
A coup attempt was planned and violently thwarted via a massacre carried out by Itachi Uchiha and Obito in secret to prevent a larger war.
5) Tanuki Shigaraki's vendetta
This one is more of a personal tragedy from Boruto, but it counts regardless. When Danzo Shimura's Root Black Ops organization was inevitably exposed to the public, all the members were ostracized by the village for years of bloodshed.
This included Sumire Kakei's parents. Sumire's mother fell ill and died soon after she was born, and her father descended into madness.
Believing that Konoha had betrayed him and being a fanatical follower of Danzo, Tanuki Shigaraki sought revenge on the village and would use his daughter to do it!
He trained her, groomed her to be a weapon and sleeper agent for the Gozu Tenno, and ultimately bound her Yokai Nue to destroy Konoha. This may have worked if not for Boruto and the rest of his class saving Sumire.
Five rivalries that assisted Konoha
1) Might Guy vs Kakashi Hatake
This rivalry brought out the best in both men and ultimately helped Konoha and each other. This was the pure embodiment of a friendly rivalry through and through, with both Might Guy and Kakashi pushing each other with races, rock paper scissors matches, and even real fights from time to time.
It's born chiefly out of Guy's need to surpass Kakashi, and the latter just going along with it.
While this rivalry technically ends when Guy's legs get broken from kicking Madara into the stratosphere, they never stop being friends or challenging each other. This is beneficial because it pushes both men to be their absolute best and ultimately do their best to aid Konoha.
It culminates in Kakashi and Guy getting the best of Kaguya and Madara, respectively.
2) Amado and Koji vs Jigen/Isshiki Otsutsuki
Although technically another Boruto entry, this one bears examination. When the Kara organization was initially founded, its sole purpose was to bring forth a God Tree and eat its fruit to gain strength and their own personal desires.
Since that got canned, Isshiki started looking for vessels as a side project. This alarmed Amado, who began plotting to eliminate the Otsutsuki from the equation.
How is this infighting beneficial to Konoha? Well, it eliminated several key pieces off the board, exposed Isshiki, and ultimately led to the organization's collapse. Koji was a clone made from Jiraiya's cells and had his sole target as Jigen/Isshiki, and it worked.
Isshiki's ultimate goal was exposed, and the elder Otsutsuki was finally brought down by Baryon Mode Naruto and Kawaki.
3) Neji's rivalries
Neji Hyuga was an elitist to the core in the original Naruto. His arrogant attitude of calling people failures and dismissing them like trash gained him a rival in Hinata (same clan), Rock Lee (his teammate), and Naruto Uzumaki (revenge for how he treated Hinata).
While Neji could ultimately handle Hinata, his bout with Naruto met a hard blow to his psyche.
Neji changed for the better following his clash with Naruto in the Chunin Exams arc. He acknowledged Hinata's strength and helped her train. He saw Lee as a legitimate threat and rival following his duel against Gaara.
As for Naruto, Neji sacrificed himself to save the protagonist and Hinata during the Shinobi World War. His turnaround helped save lives, and his sacrifice helped turn the tide of the war.
4) Gaara vs Naruto (and Kurama vs Shukaku by proxy)
Gaara was like Naruto in many ways. They were ostracized by their villages, seen as aberrations, and both had monsters inside of them that likewise hated each other.
The Tailed Beast rivalry extended since way before Konoha was ever founded, back to the days of the Sage of Six Paths. When the two met in combat, Kurama and Shukaku's egos and tempers were enough to destroy entire forests!
However, the two-tailed beasts would bury their particular hatchets during the Shinobi World War and Boruto. Naruto likewise helped Gaara out of his darkness during the Chunin Exam arc, seeing him become Kazekage and even helping rescue and revive him!
It blossomed into a friendship that has lasted well into Boruto and has proven excellent for relations between Konoha and Suna.
5) Naruto vs Sasuke
Where to even begin with a longstanding rivalry like Naruto vs Sasuke? The two have been at each other since their schoolyard days before the Academy.
Once they graduated, all bets were off when they were on the same team, having to learn how to work in sync and keep their respective problems with each other in check. It appeared to work for a while until Sasuke's defection.
From that point on, they took out members of the Akatsuki, discovered the secrets of the Uchiha Clan, and eventually teamed up again to prevent the world from being destroyed. The aftermath of their final fight? Them growing up to be dads?
They only made the world better by continuing to fight the Otsutsuki clan and be there for their kids, though not without growing pains.