“There ain’t no sky today, probably forever,” said the commander of the United Force. The sky distinctively darkened. The black inky object gradually penetrated through the blue sky, following the overwhelming noise puncturing eardrum. The once blue and clear color vanished quickly, while the dark, inky starship occupied the once warmed and bright sky. The once thriving mankind was now threatened by the outside enemies with unknown and relentless power, who were now rushing towards the seemingly solid defensive system.

Two years ago, humans found the exo-planet outside the Solar System. Unlike other planets that are far away from Earth, this planet was only 1 light-year from the Solar System. It was a tremendous distance for humans in the past, but recently because of the technological breakthroughs, interstellar immigration was no longer an imagination.

Countries urgently scrambled to send satellites exploring the new residential planet. It seems that the targeted planet is a better version of Earth with larger size and more abundant natural resources. The dispatched satellite delivered images of the exo-planet with data analysis and geographic information back to Earth. While people were analyzing the general information of the exo-planet, they unexpectedly discovered living traces of high intelligence species on that planet. Before humans embraced the fact that they are not the only high intelligence species, the aliens noticed Earth’s humans. They sent undecipherable and unknown symbols and words. No one could understand what the aliens wanted to express as well as their potential attitudes towards mankind. Many people worried about being attacked by the aliens. Despite the potential threat of being attacked, human beings still expected to get friendly messages from that planet. Some countries send satellites to communicate with them. Nevertheless, the other planet attacked the explorer satellite, responding with the massive starships with no goodwill.

While the Earth seemed to be in chaos for a short period of time, countries gradually corporated each other against the huge enemy. A united government led by the United Nation was established. Countless troops and soldiers were allied and waiting for the potential threats from the universe. It seems that the Earth’s fate was determined at this moment. Indeed, the tremendous starship did operate military attacks before reaching the Earth. Cities were destroyed, leaving with corpses and ruins that reflect the alien’s ambition of conquering the Earth. After the threatening attack, the United Government fought back. After a fierce battle, it seemed that the aliens’ technology was much more modern and powerful than the Earth’s. The United Government found out that those enemies were extremely fragile. The aliens’ skin couldn’t be exposed to the air or sun, or they could be burnt and died. Most importantly, those protective layers on the starships and the armor of the alien soldiers could be destroyed by the mixture of acidic substances. After a few accurate but sacrificing battles, the once invincible enemy suffered heavy losses. They were forced to surrender and captured by human beings.

While human beings celebrated the victory, the satellite detected another fleet of alien starships charging towards the Earth. Some country leaders might worry that mankind would suffer again from the aliens. To everyone’s surprise, the tremendous starship didn’t operate military attacks while reaching the Earth. When the united force prepared for the first attack, the aliens conveyed a new form of communication, involving weird languages and friendly gestures. Each countries’ leader, stunned but hopeful, agreed to meet with alien representatives. Slowly, humanity began to realize that the extraterrestrial visitors came for an alliance, which was not the same species that attacked the Earth. The friendly alien implied that the one that attacked the Earth was also attacking the friendly alien’s planet, and they came here for potential alliance against the unanimous enemy. After a period of discussion, the United government agreed to form an alliance and signed a treaty about it. Since then, the two species fought with each other against the common enemy, until the enemy species totally controlled the two planets.