Gate: Thus the Bundeswehr strikes against tyranny

The world of Aurelia was once a small unimpressive world, double the size, width and mass of Terra, but keeping the same gravital pull of our blue planet. But, tyrannical eyes have set upon the small principality of Matador. Once a grand empire that was both respected and feared amongst its adversaries, stretching from one continental side to the other, conquering and subjugating tens of thousands of people and demi-humans, even the High Elfs, it fell due an unknown power appearing from nowhere, with many claiming them to the worst enemy they had ever faced, worse than the rumored Demons in the Unknown, foggy continent.
This unknown force, called the infamous "Grey/Black men", clad in two Lightnings and death skull emblems, only made the life of many sub-humans worse, killing dozens per minute or even seconds. Only through the sheer tenacity and change of situation back home, forced the unknown superior military to conceded and retreat back, leaving tales of destruction and heresy back in this now peaceful world.
One hundred years later, the newly emerged Superpower of Atlantia has begun expanding its influence in other continents, including the once isolated continent of Aurus, once ruled by Matador. Playing their cards right, they gained sympathisers and backstabbing people amongst the ranks of the elite and hierachy, further strengthening their hold in the new continent.
Ravaged by greed they invaded the isolated Principality, seeking to dethrone the Princess and putting her Regent into power, turning the vast continent in one giant vassal, with its minions doing the dirty work. In a last desperate move the Princess attempts to destroy any evidence of the Gate, a connection to two worlds, the black men's home world, but alas, this failed. Consequently, greed had its price and the Gate fell into hands of the Alliance. How will the other side fare and will peace return in this tyrannic world?