The great rebellion of Aztlan seemed to be coming to an end by December 2134. The rebel capital was forced to relocate to Phoenix, Arizona after the Union victory at Denver. Utah, an autonomous state in Aztlan, went so far as to sue for a separate peace on May 11; with victories in Texas and California, Aztlan’s few remaining forces were left to prepare Phoenix for siege. As Union forces prepared to surround and capture Phoenix, and perceiving a Union victory as an external threat to Mexican sovereignty, Mexican president Edwin Jaso issued an ultimatum to the US: turn back now or face a larger war. Many northern Mexicans supported Aztlan’s bid for independence, and under the dual citizenship program, the Aztlan rebels were technically Mexican citizens. The US ignored Jaso's ultimatum, and upon entering the outskirts of Phoenix, on December 9, 2132 Mexico detonated its nuclear arsenal along the DMZ to clear a path to invade the American Southwest, killing 10,000 US military personnel during the attack, and destroying the majority of American tactical nuclear weapons. Upon reaching Phoenix, Mexican forces were met with cheers from many citizens and silent awe from those unsure of what this war now means. Bombardment from the Mexican Orbitals, and advanced ground based defense systems severely reduced the American ability to respond, leaving fighting primarily on land and at sea. With US allies and worldwide forces engaging Mexican client states in Eurasia and Africa, few reinforcements could be recalled to defend the homeland, and by the end of 2135 Mexico had advanced as far north as southern Oregon, Idaho, and Colorado.
After pushing US forces as far back as Denver, and destroying the US Naval blockades whilst creating their own around New Orleans and Ecuador, President Jaso arrived in Santa Fe on November 19, 2135, declaring the rebel American states to be Mexican territory and committed to secure the territory lost to the US in the First Mexican American War, almost three centuries ago. Many Mexican-Americans that had supported the Atzlan rebellion were opposed to outright annexation, and formed independent resistance groups, while previously neutral citizens sided with the Union. With Mexico poised for critical victories on the homefront, and US forces tied down abroad, on November 25, 2135, President Lionel Halvidar lifted the self-imposed ban on using bombardment weapons on US territory and began striking Mexican held assets in the South West. Orbital bombardments by Mexico and the US were constantly being interrupted by both sides’ space forces, leaving the fighting on Earth largely to terrestrial forces, but the American bombardment campaign had finally stalled Mexico’s advance.
With their allies advanced stalled in Ecuador after American reinforcements arrived from Machupe and Australia, Mexico began to seek an ally to limit the ability of the US to move forces even further. In a secret meeting in Athens on January 9, 2136, Mexico and Poland agreed to ally against the US, with Mexico guaranteeing Polish dominance over Northern Europe, and Poland agreeing to engage the US directly to limit any movement of potential American forces to reinforce the homeland. On January 25, 2136 Poland entered the war with Mexico pulling the US into a protracted war across the planet. Mexico had also succeeded in a blocade and limited invasion of the Moon, depriving the American war machine of its most immediate source of Helium-3. The blockade, and subsequent invasion of key Lunar assets, were resisted by the US Lunar Guard and local Space Force personnel, but with the majority of US Space Forces committed to Earth Orbit, Luna's forces were only able to limit Mexico's access to Helium-3 supplies and shipyards, rather than retaking them for the US. US forces in the Americas were now left with no hope of reinforcements from abroad and were operating under power rationing, leaving US-Allied forces to operate under Fabian tactics to do little more than slow Mexico’s advance.
As Mexico secured its gains in the Southwest and left American forces stretched thin across the planet supporting their allies, President Halvidar initiated a bold strategy. Just after assuming office and granting statehood to many colonial territories, President Halvidar used his executive powers to seize a fleet of incomplete ships, built by the colonies during the Second Martian Revolution, as vessels of the US Space Force. On August 11th, 2136, Halvidar nationalized the Planetary Guards of the colonies and called them to defend the Homeland in what would become Operation Stardust. The colonies used this secretly constructed fleet to speed toward the Earth to relieve US terrestrial forces. The ships were outfitted in what was the latest in military hardware, including next generation Space Force armor that were capable of re-entry and orbital flight. Mexico detected the fleet on August 24th, and on August 27th the first wave of colonial forces would reach Earth. Hoping to end the war before the American colonials arrived, Mexico launched a daring attack of its own on the US capitol of Washington D.C., detonating a nuclear flare above the city and invading from orbit on August 26th. With the remaining domestic naval detachments engaged with Mexico in the Gulf, and Army forces fighting to hold onto territory in the Rockies, the capital was largely undefended. Mexico deployed a force of 20,000 from their Orbitals, in a battle against 5,000 US reservists that would ultimately be a turning point in the war.