Military action
Fed up with the fighting, Highriders at O'Neill Two declare independence, using deltas and scavenged mass drivers to drop dozens of lunar rocks and other "ortillery" at key sites all over the planet, causing widespread death and destruction. U.S. and Japan officially recognize the new government.
The Highrider "revolt" that later became known as the Seven-Hour War was a decidedly well-organized and planned event: it soon became obvious in retrospect that the space-dwelling colonists had been preparing to break away from their ESA masters for some time, and the War only provided the excuse. A question that has plagued many post-War historians has been "Where did the Highriders get the materiel, knowledge, and training to deploy such weapons?" The short answer is no one really knows; but if you spend most of your time shuttling mass driven cargoes from Luna to orbit and back down to Earth, chances are that you will become pretty adept at calculating delta V and other components of ortillery; including the ability to make your own. If the alternative is to have your fragile life-supporting habitats blasted to shreds as sacrificial lambs in the middle of a raging space battle between Corporate forces, you learn really fast how to protect yourself. So before either side could move their war into space, the Highriders began to hit both sides with their own lethal suborbital "ortillery" strikes capable of wiping out most of a small city, as well as wiping out the Corporations' own orbiting satellites. When the dust settled, the Highriders announced that they would henceforth consider themselves an independent nation and neutral in the ground-side conflict. Or else.