The battle of Mutal (Tikal) in 682. Few battles have been so climactic.
The Central Maya states were in the true "Forgotten War" of history--a hundred years of on and off warfare that amounted to an eipc struggle between Mutal, and Kaan, the kingdom of the Snake, now known as Calakamul. The casus belli was when Mutal was invaded by Teotihucan of the central Mexian valley, who set up a puppet ruler. This puppet king of Mutal set out to control the entirety of the central Mayan principalities.
The king of Kaan was determined not to let this happen, and managed to form a ring of vassal states around Mutal--he both surrounded Mutal and got himself a dominant position in the heartlands of the Maya in a single stroke.
These forces advanced, destroyed the city state of Mutal, installed a puppet king, and saw the rise to greatness of Kaan.
However, Mutal would not be so easily cowed, and led a rebellion against the Kaan. Against all odds, they succeeded, driving the more numerous and powerful armies of Kaan back to their capital, and the future of Mutal seemed secure. But though they had annihalated the threat of Kaan, worse was in store.
The Mayan states were islands of inhabitable land in a salty swamp, more or less. They created fresh water by pouring crushed limestone over the salty sediments in the bottom of the water, and thus having good water to grow crops. But it was a precarious system.
The Hundred Years War of the Maya was what pushed it over the edge. Thousands had died in those vicious battles, and the water beds went relatively un-maintained. Combined with vicious drought, the Mayan heartlands collapsed. The great cities of Mutal, Kaan, and Oxwitza were obliterated, slowly being reclaimed by the jungle. The millions of Maya who had lived in the heartland of their realm were reduced to thousands. The center of Mayan civilization shifted to the north, under Chichen Itza.
You would be hard pressed to find a more glorious, devastating war, anywhere.
EDITED out some rather embarassing errors.
