The empire existed as of six hundred years ago, though there's some indications it was in its second dynasty. There's mentions from that time of a golden age three to four hundred years prior, but frustratingly little actual information.
The empire had assorted rises and falls over the next three hundred and fifty years. Shinobi became a notable force mostly in the last century, as chakra-trained mercenaries who could challenge even well-trained samurai. Some of them were probably rogue samurai, some self-taught, some monks who broke with their traditional pacifism...
There was a civil war that started two hundred and seventy years ago. The Emperor died in it, along with all his children and grand-children and nieces and nephews, with a somewhat suspicious thoroughness. The daimyo started warring among themselves for the seat, but then people started trying to overthrow the daimyo, and the provinces fragmented.
Ninety six years ago, the Senju and Uchiha clans were the two most prominent and powerful shinobi clans in Fire - and they were sworn enemies. Two shinobi of great future note, Senju Hashirama and Uchiha Madara, were likely born this year. Both lost assorted unnamed and unnumbered brothers to the fighting. Uchiha Madara had no known living brothers; Senju Hashirama had one, Senju Tobirama.
Sixty three years ago, Senju Hashirama and Uchiha Madara united their clans to form the Hidden Leaf. This allowed them to pool defensive resources, and demand fairer contracts from clients. Other clans quickly joined them, and within the decade many other clans in other nations had formed their own hidden villages.
Within a few years of the major hidden villages forming, the first Great War happened. Historians generally consider the Great Wars to be a natural outgrowth of increased consolidation. The first Great War lasted ten years, and by the end of it all of the early hidden villages were on their second or third leader. The second Great War started when everyone was on their third leader, and was the longest. It saw the destruction of Uzushio and several other nations. The second Great War was also when the mainland started fielding child soldiers again. That'd been a practice the early Leaf put a decisive end to, but by the time the third wave of leaders was in power no one really remembered the constant wars and early deaths of the Warring States period.
The third Great War was the most recent, ending sixteen years ago, though there was some scattered clashes for a while afterwards. It saw the rise of several place's fourth leaders.
There's a timeline of the known leaders and their policies for the most notable nations, especially the big five (Leaf in Fire, Mist in Water, Sand in Wind, Cloud in Lightning, Rock in Earth).
The current leader of the Leaf is their fifth, Senju Tsunade. She's noted for heavily advancing medical research. The current leader of the Sand is their fifth, Gaara. He's noted for being extremely young (Sasuke's age, in fact) and an advocate for peace. The current leader of the Rock is their third, Oonoki. He's old, and is known as the 'fence-sitter.' The current leader of the Cloud is their fourth, A (though this is a traditional name all leaders of the Cloud have taken on). He is known for being passionate and a bit of a war-monger.
There's also a timeline for the Land of Snow. They united fairly late, out of wandering tribes supplemented by samurai who had left the fighting. They technically have a hidden village, but unlike in other nations theirs is fully integrated with the main nation. Thirteen years ago there was a coup, and the current Queen's uncle killed her mother, taking the nation for himself. The then-Princess was spirited away by loyalists, though her younger sister vanished. Three years ago, the Queen killed her uncle and returned to power. A Leaf team helped, mostly in guarding the Queen during her journey back. Snow has good trading relationships with Fire, but some of that's hampered by Lightning, which guards the easiest sea-route and which is hostile to Fire.