Taken from: en.wikipedia.org/wiki/Robotech_Wars

Final Battle

When Breetai approached the SDF-1, there was some initial mistrust severe enough to have the Micronian's newly repaired main gun on a hair trigger. Again, Khyron nearly ruined the incident by launching an unauthorized attack on the ship that almost provoked the Micronians to fire. Only when Breetai had the fighter group destroyed were they convinced that the peace offering was serious. As Exedore parlayed with the SDF-1 crew, Dolza assembled the Grand Fleet to eradicate Humanity and the corrupted Zentradi. When Exedore was informed of this development, he immediately advised the Micronian ship to flee the solar system, which the loyal humans rejected out of hand. As Gloval's ship and the dissident Zentraedi led by Breetai and Azonia prepared for battle, Khyron fled against the seemingly impossible odds. Almost five million Zentraedi warships folded to Earth in response to Dolza's orders.

The main Fleet began a massive planetary bombardment of Earth, eradicating almost every large population center and devastating most of the planetary surface. The area devastated was "95% of the Earth's surface" according to the series narrator.[6] Another account from the supreme commander of the planet's forces later quantifies the devastation by numbering some "70,000 survivors of the Zentraedi holocaust." Alaska Base, which survives the initial attack, fires its superweapon - The Grand Cannon, which destroys a large portion of the Zentraedi fleet. Following this attack, the SDF-1 and the allied Zentraedi Imperial Fleet launched an attack of their own, using the music of Lynn Minmay to confuse the forces of the Grand Fleet, then blasted their way into Dolza's massive planetoid homebase using the Daedalus attack. Once inside the vulnerable centre, the SDF-1 launches a massive quantity of missiles before engaging its defense barrier to maximum power. Dolza is last seen watching video of Minmay singing "We Will Win" before the planetoid homebase explodes, with enough force to destroy the rest of the Zentraedi fleet, ending the First Robotech War.