In the wake of the Ga-yahkra, Ga-Metru was sent reeling, sympathy for Ta-Metru rose, and unsurprisingly, Ga-Metru officially allied itself with Ta-Metru. Ta-Matoran soldiers are ferried up the coast once again, this time to the Assemblers’ District, where the Ta-Matoran rapidly establish a beachhead. The Po-Matoran and their allies quickly abandon the district in favor of their more defensible cliff fortresses in the Sculpture Fields. Ga-Metru Privateers begin pick off all transports inbound to Metru Nui, their resources flowing into the Ta-Metru forges and new armaments flowing out. The Le-Metru hit-and-runs grind to a halt as Ta-Matoran tear down the highways connecting their two Metru.
In the year 20,551 Po-Metru redeploys their Navy, having finished fortifying the coast of the Wash; first attempting to blockade the Ga/Ta-Metru coasts, but quickly finding they have nowhere near enough ships, they then set out on a relentless offensive on Onu-Metru. The Le-Matoran transports that had once crossed Onu-Metru to reach Po-Metru - now resupplied and carrying Po-Matoran reinforcements - slam into the Onu-Matoran front near the coast, supported by the Po-Metru Navy. The Ko-Matoran launch their own offensive on the other side of the Onu-Metru coastline, creating a pincer formation that allowed them to quickly take control of the Onu-Metru coast. They then begin to slowly force the Onu-Matoran inward, out of their own Metru. The Seige of Onu-Metru would last for over a year and claim countless lives, but in the end the Onu-Matoran had no choice but to abandon their home and seek refuge in Ta-Metru.
Throughout the entire war, Le-Metru had remained mostly untouched, acting as the backbone of the Po-Metru war machine with no recourse, but Ta-Metru is done letting Le-Metru blaze their way across the island. The March of Fire begins with Ta-Metru redeploying their idle troops from the Assemblers’ District through the rails, down to the Ta-Metru border. From there they begin to push their way into Le-Metru, burning a path to the Moto-Hub with one goal: put a stop to Le-Metru’s seemingly endless supply of transports. Another force deployed to the Le-Metru coast in Ga-Metru ships, looking to carve their own path to the Moto-Hub and catch the entire Metru in a pincer formation of their own. They get caught about a kio inland and clash with enemy forces in the Battle of Le-Metru, eventually attaining victory, but the delay would prove costly. Although the Ta- and Ga-Matoran blaze their way across Le-Metru, the Battle of Le-Metru had cost them valuable time. The last vehicles out of the Moto-Hub are large, powerful transports built to carry the smaller, faster Le-Matoran transports over the jagged Ta-Metru border, releasing them into enemy territory before the Ta-Matoran can react. It was time for Operation Muaka, the last maneuver the Le-Matoran planned in their own Metru. The quick Le-Matoran transports lead the Ta- and Ga-Matoran soldiers on a massive chase across both Ta- and Ga-Metru, cutting the unguarded train lines to the Coliseum inland, before reaching refuge in Po-Metru. The Ta- and Ga-Matoran armies finish taking Le-Metru, most of the remaining Le-Matoran having fled into Ko-Metru; they would forever remember this as Tagaki-ya, “the Days of Great Burning Waves.”
Now the island was split in half, a single front running down the length of the Great City. The war would continue for another 300 years - countless battles would be fought, unimaginable numbers of lives were lost - but none of it would matter. The Great City had descended into gridlock, no side able to gain any tangible advantage over the other; they became trapped in what would become known as the Great Stalemate, and they would remain that way until the intervention of the Makuta, and the Archives Massacre.