Aldnoah Zero

In 1972, an ancient alien hypergate was discovered on the surface of the moon. Using this technology, humanity began migrating to Mars and settling there. After settlers discovered additional advanced technology, the Vers Empire was founded, which claimed Mars and its secrets for themselves. Later, the Vers Empire declared war on Earth, and in 1999, a battle on the Moon's surface caused the hypergate to explode, shattering the Moon and scattering remnants into a debris belt around the planet. Cut off from Mars, the remnants of the Vers Empire established several massive orbital space stations within the debris belt and a ceasefire was established. 15 years later, in 2014, an attack on the Vers princess during a peace mission causes the Empire to launch a new attack on Earth, this time determined to conquer it once and for all.