In the year 2030, Eric and Kyle Johnson had a dream. They wanted to prove the existence of a Spirit Realm. Through many years of meticulous planning, the brothers constructed their first prototype interdimensional portal unit. Its first test proved to be a failure, or at least that's what they thought. They'd opened a gateway, and the only problem, once a gateway had been opened there was only one possible way to close it. Destroy the unit completely.
The United States Government knew of the unit's existence, and that it was a success. So they stole the unit, before the brothers could destroy it, in the hopes of entering the dimension beyond the gateway. Upon breaking the barrier between our world and the next, they released Death in physical form. He'd been waiting for centuries to be set free, biding his time, building his strength. This was the beginning of the end for our Earth Plane of existence as we knew it.
The brothers banded together with various survivors, to find the portal unit and destroy it. It was the only way to send Death back to his dimension for good. Death was ahead of them at every step. He'd raised the world's dead, to roam and feast upon the living. Managing to bring across a vast demonic army before the brothers destroyed the prototype unit. As Earth slowly died around them, Death wanted another unit built. He wanted to release Satan himself, and thus jump start an early Apocalypse. The Johnson brothers and their party of survivors fought until the very end. They managed to destroy the second unit, and stop Death, Kyle lost his brother and party. There was but one survivor that remained with him in the end.
The year is now 2050, Kyle made a trek across the United States ending up in Washington DC. The zombies had not returned to the Spirit Dimension, for they hadn't come from the portal. Kyle spoke to the President of the United States about the devastation plaguing the Earth. He knew and had set into action a constituency plan. Government scientists had been hard at work since the first incident - known as the Dead War - creating a vast ectoplasmic barrier system that would force the dead and other creatures to one, less populated side of the planet. This force barrier was known as the Demonline. The known armed forces were combined as one elite fighting force - the Brimstone Brigade.
The world seemed to be getting back under control. Until a madman known only as Obsidian, fled to the evil side with the blueprints of the Johnson Device. The blueprints that were supposed to have been destroyed completely. Obsidian was a genius and knew how to boost the power of the device a hundred fold. Since constructing and opening the portal again, unholy creatures have poured out of the gate, and threaten to tear through the Demonline. It's up to the Brimstone Brigade to see that he's stopped once and for all. And so their struggle continues to this day.