Following the bloody One Week Battle, the Earth Federation and Principality signed the Antarctic Treaty, forbidding the use of Nuclear, Biological, and Chemical (NBC) weapons. While this narrowed the range of strategic options, it also gave a distinct advantage to the Principality Army, whose plans were centered on use of Mobile Suits. One week later, the Principality commenced its assault on Earth itself, using the Mass Driver, an electromagnetic "catapult" on the lunar surface, to send their MS into space and Earth.
The Principality's Earth Attack Force, led by Garma Zabi, was divided into five MS divisions with distinct goals. The first group dropped on Central Asia, wiping out the Federation's Baikonur spaceport. They then advanced to the Caspian Sea, moving west into Europe and south into the Middle East.
The second and third groups were dropped on both coasts of North America with two objectives: 1) To subjugate the Federation's industrial military complex. 2) To take over the Federation food supply. The California Base (a generic term for the more than 20 military bases along the west coast) became the staging ground for subsequent terrestrial assaults. As the bases were captured without damage, they were soon converted to serve as the new Zeon Earth Attack Force headquarters and production facilities of Zeon MS.
The fourth group, aided by support troops already on Earth, occupied many islands of the Oceania region for the procurement of resources. Up until then, the Principality faced a distinct disadvantage in resource availability, having to rely on Lunar and asteroid mining.
The fifth and final group landed in the largely unprotected deserts of North Africa. With facilities, food and resources at their disposal, the Principality was set for global conquest.
With the Federation forces scattered and their numbers decimated, their outlook was grim. A chance to strike back opened up with the death of Garma Zabi. Operation Odessa used 30% of the Federation Army to take out the Zeon mining facilities in the Odessa region, the lynchpin of the Principality supply network. From there, the determined Federation emancipated Europe, Asia and eventually North America. The remaining Zeon troops regrouped for a massive assault on Jaburo base, hoping to kill the heart of the Federation. When that failed, only the Zeon troops in North Africa continued their resistance.