"I am a Ghost, an elite soldier. Trained to strike my enemies, before they even know I exist. Death stalks me, but I survive, overcoming any obstacle, never surrendering. And with my brothers and sisters at my side, there is no fight we fear."

"We are Ghosts. We aren't afraid of death. So, when you take the lives of my brothers, when you provoke me...It doesn't matter how powerful you are...I will burn your world to the ground!" - Anthony "Nomad" Perryman, Leader of Ghost Recon Team Kingslayer.
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It has been three months after the coronation of Twilight Sparkle and the defeat of Lord Tirek. The Elements of Harmony and the newly-titled Princess of Friendship have settled back into their daily lives in Ponyville. The realm of Equestria has been returned to a state of peace and harmony. Until everything that Celestia and Luna had hoped to see come in this age...was lost.

An invasion of Equestria, launched by the armies of the southern land of Eqaharia, conquered the realm. The Elements of Harmony scattered, Twilight Sparkle captured, and the Royal Sisters exiled. The Crystal Empire, the last free nation on the continent of Equus, besieged. All hope seemed lost.

Until they came. Sixteen in number, trained to be the elite, armed and bolstered with the full power of the US Military. They will not stop until Equestria is free. They are the Ghosts. They will not fail.
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Ghost Recon: Future Soldier, Wildlands, and Breakpoint crossover, set in an AU of Season 4 of FIM.

Roster of Ghosts and their weapons can be found here.