Mobile Suit Gundam AGE: Story of the Beginning  

Kidou Senshi Gundam AGE: Hajimari no Monogatari, 機動戦士ガンダムAGE 〜始まりの物語〜

The Space Age started when humans settled in space colonies and lasted for hundreds of years. Although there was initially peace, it didn't last long as an unknown enemy appeared suddenly, leading to a war that has been ongoing for a century now.