From EVE History

Precedents:

The wars had one major precedent, that ignited the conflict: The Bleak Lands Campaign, during which the Minmatarr rebels lead by Karishal Muritor started to wage an open war against the Empire. There were two of those campaigns, sepparated by several months, and they gave the Minmatarr the much needed knowledge for their actions in the upcoming war.

Also, it should be taken into account that the Caldari had conquered and settled a new region bordering with the Gallente, without the knowledge of the Federation.

The Begining:

The two storylines start sepparately. First, the Gallente started it by destroying a Caldari station where an important diplomatic meeting was taking place. This allowed the ascension of Tibus Heth, who slowly turned the State into a war machine capable of turning to the offensive, instead of the defensive. And second, the Mimatarr took down the Yulai CONCORD station, takig down their defense grid for some hours. With the grid down, both the Minmatarr and the Caldari launched massive war operations against the Amarr and the Gallente respectively.

The Minmatarr were hugely succesful for some time, conquering some systems and freeing thousands of slaves. Even more, the Insorum was given to them, freeing them from their addiction to VITOC. The Amarr Navy entered combat to stop them, but the battle reached a stalemate, where none of the sides could turn the tide to their favour. This was broken when Jamyl Sarum, seemingly returning from the dead, appeared in the system and laid a blow against the massive fleet assembled by the Elders, effectively destroying most of their ships and forcing the rest to flee chased by the Navy.

The Caldari, on their side, launched a major assault directly on Caldari Prime, being their goal to conquer the planet. The battle was quick and bloody, and soon the Caldari had conquered the planet. President Foritan quickly negotiated a peace with Tibus Heth that gave the Caldari ownership of their core planet once more.

By then, the CONCORD grid was put back online, and CONCORD forced the warrying Empires to back down. It activated a legal clausule that stated that war between the Empires can only take place through pod pilot militias, and thus Faction Warfare started, and the Empyrean Age begun.

The War:

Little is yet decided, but many factions have rallied to join all the sides of the war, quickly scoring initial points in some systems or others. Meanwhile, Lady Jamyl Sarum has been confirmed as the next Empress of the Amarr by the Heirs and Theology Council, while Maleatu Shakor was named head of the Minmatarr Republic without opposition.