Was undeclared. Exactly where and when it began is debatable. Most would say there had been low-level conflict for millennia, but it only became a world war toward the end of the 20th century CE. Some choose the symbolic date when we ran that tanker, the Exxon Valdez, aground in Prince William Sound, because its cargo was the secret weapon that had brought the war into this new stage.
Our global forces were still divided into two antagonistic camps at that time, but both were at war with the greater enemy. The eastern camp had already killed the Aral Sea and poisoned 180,000 square kilometers of land with nuclear radiation (although this action was a Pyrrhic victory, resulting in more drastic consequences to us than the enemy). Shortly thereafter, we declared a truce of sorts between the factions, so we could make further gains in the great war, ostensibly without so much damage to ourselves. For the remainder of the last century, our forces were on the march everywhere, and the enemy fell back.
But in the early years of this century, some unseen fulcrum began to shift. Rather than the widely and randomly interspersed events we experienced in the relatively mild regime we grew up with, we saw destructive actions that escalated in their scope and frequency until they came to seem like calculated responses.
The waves of heat and cold. They caught us off-guard with their new intensity. Then the storms, to which we continued to give bland, suburban names: Mitch, Dennis, Katrina, Irene, Sandy, Iris, Maria. At first mostly a threat to the growing legions of the unprotected poor, they soon showed themselves a match for our largest cities. And beyond that: whole provinces, countries were paralyzed for days, weeks, months. And then the fires – early on they were far from where we lived and breathed, in the still-vast northern forests, but then they came closer, filling the skies of our cities apocalyptically with drifting ash and smoke, and finally, audaciously, striking at the sprawling cities themselves, taking thousands of buildings in a single attack.
Our initial casualties were so small – a few tens of thousands a year against all our billions. We published the tiny body counts for each incident, as if nothing else was of consequence. But overall, we took little notice, because we killed ourselves with friendly fire in vastly greater numbers. And against the enemy, we unleashed a holocaust. Total war. We took no prisoners. It was xenocide; we were willing to exterminate not just individuals but whole species to win our freedom. Thousands, then tens of thousands of species began to fall.