The Secret History of the Mongols was written for the Mongol ruling family shortly after Genghis Khan's death, and is largely a biography of Genghis Khan. It's been a few years since I've read it, and I will defer to our East Asian historians as to its accuracy and how it was transmitted to the present, but I highly recommend it at least as an antidote to the idea, which seems prevalent among Europeans and their descendants, that Genghis Khan is some sort of bestial character. Genghis Khan was ruthless, his wars bloody, and his campaigns world-historical in their scope, but as a military leader he was very much a product of his time and his upbringing.

Before he was known as Genghis Khan he was born and grew up as Temujin. His father was leader of the Mongols, who at that time was one of a number of tribal groups in what is now Mongolia. His father was killed by Tatars, a competing tribe, and Temujin and his family spent a long period in extreme poverty, before Temujin was able to slowly win greater power with his Mongol tribe, and once leader to defeat neighboring tribes (the Tatars, Naimans, Merkits, Keraits, and Uyghurs).

Temujin slowly built up a group of subordinates who had demonstrated talent and loyalty to him, as well as promoting able talent within his own family. He wasn't also averse to using assistance from the Jin, who were a Sinicized Jurchen people ruling an empire in the North China Plain.

When Temujin finally unified the Mongol Confederation of tribal peoples in 1206/1207 and was proclaimed Genghis Khan, he set his sights on conquering the North China Plain, much as the Job themselves had previously done. Mongol expansion and pursuit of defeated enemies also led Genghis' armies westwards, most notoriously against the Empire of Khwarezm, a Muslim state ruling much of Central Asia and based in the delta of the Amu Darya near the Aral Sea.

The Khwarezmian governor in the city of Otter had atracked and killed a caravan of Mongol envoys, and Genghis Khan took this as an affront to be punished mercilessly. Most of the infamous massacres in Genghis' campaigns occurred at this time, and involved the wholesale destruction of cities such as Samarkhand and Bukhara, as well as their inhabitants.

But with that said, I also need to emphasize that Genghis wasn't merely hell-bent on killing. Peoples who surrendered to the Mongols were (by and large) spared, and often taking into Mongol service and administration - the Uyghurs of the Tarim Basin are a prominent example of this, and served as able administrators of the Mongol Empire throughout its existence.

While many further bloodly campaigns such as the Sack of Baghdad or the Sack of Kiev were undertaken by Mongol armies, I should emphasise that these were led by Genghis' descendants after his death, so they fall outside the scope of the question.

Overall, the main difference between Genghis and his contemporaries was the scope and scale of his wars and conquests. His Western campaigns against the Khwarezmian Empire is probably an exception in terms of brutality, but here too it was not something completely irrational: the Khwarezmians had violated norms around treatment of envoys, and Genghis considered this a war of punishment. The explicit brutality was in part a deliberate strategy of terror: the Mongol forces were hoping that bloody massacres and reprisals would encourage quick surrenders of cities as inhabitants tried to spare themselves such a fate, and conveniently also spare the invading Mongols long and costlysieges.

You really have to see his life to understand.

1. He was the son of a stolen mother. That’s how it starts.
2. His father already had a 1st wife and 1stborn son.
3. His father takes him as a boy on a journey to find a family that will take him in to work and marry a daughter (to prevent the sons from fighting most likely)
4. His father gets poisoned on the way back home, requests his son to come back but dies before his son arrives.
5. Now the family of 7 gets robbed of their animals and kicked out of their group because they don’t have a man to help hunt/protect the group and have to many mouths to feed.
6. Genghis mother goes out hunting for small animals and digging out roots desperately to feed the family. The boys pick up quickly and start hunting and fishing themselves.
7. Genghis older step brother is now in charge of the family and has been taking food from genghis and culturally will soon be able to take genghis mother as his wife.
8. Genghis and his younger brother make a plan to kill their step brother. They shot him with arrows. They spared the younger brother because he had no fault. (To me this shows ability to judge character)
9. The tayuchiud in control of this area captures him for the killing and to stop whatever he might try to do next. They strapped him in a cangue.
10. He escapes and a family helps him remove the cangue and escape.
11. He finds his wife still waiting for him
12. They get married
13. The merkid (group that genghis mother was originally from) decided to take revenge for her kidnapping a generation ago and kidnapped genghis new wife.
14. Genghis requests the help of of the Kereyid Ong Khan and his best friend Jamuka. Together they get his wife back and loot the merkid.
15. Sounds like a happy ending but they soon find out that genghis wife, borte, is pregnant.
16. Their son Jochi would be the reason the empire couldn’t stay together after genghis died. No one believed he was genghis real son, but a merkid bastard.

Now this was off the top off my head. By #16 he’s not even 20 years old. He goes through more betrayal and failures before becoming the famous man we all know him for.

He was definitely not desperate for war. He was not mentally ill. If anything, he had mental trauma and post traumatic stress.

Anyways If you respond we can go more in depth.