A/N: Quick Disclaimer- this story is pretty AU. There won't be any mention of the original Clans or any characters from the series. I hope that doesn't deter anyone!
Prologue
Shadows streaked the grassy plain, chasing each other playfully in the moments before dawn, when no light intruded to spoil their fun. Stars glittered in the sky above, peaceful, serene. A breeze floated by, bringing the sharp scent of windblown grass to the cats perched on the small hill.
"Froststar," a dark she-cat murmured. "I'm all for the plains campaign, but are you sure about the next place? The forests to the north have a far more… hospitable climate for us." Her wry voice carried subtle hints of sarcasm. Froststar smiled at his deputy, his cold blue eyes glittering in the starlight.
"I am sure, Blackflash. OneClan must conquer all the territories we encounter or face the consequences of an attack. This is a border we must secure, and the desert is no less important." The deputy's green eyes narrowed in a dangerous smile.
"Then let's get to it," she mewed, controlled excitement and wry humor mixing in her tone. "Shall I give the order to move out?"
Froststar looked out over the sweeping grassy plains and wondered at the news his scouts had brought him earlier. A vast desert, they had reported. Sands that stretched beyond the horizon, sun that scorched the fur from their backs. What cats could survive in such a place? Even his old home in the mountains had not projected such an inhospitable appearance… He stood with simple majesty, the breeze gently ruffling his fur only adding to his own confident bearing. His broad, muscular shoulders were never bowed, his huge paws never unsteady. Blackflash looked up at him with adoring eyes.
He finally turned back to her. "I will give the order," he said with a smirk. "I will be remembered in the stories as the leader who began the glorious western campaign. We shall sweep across the plains and conquer even the shifting sands with our cause. Mark my words, for one day our exploits will be written even in the stars." Blackflash drew herself up proudly, a smile spreading across her striking features.
Froststar turned to the collected cats arranged from behind him. They were the strongest of warriors, his own personal army. Each was from a different land conquered in the name of OneClan. Forest cats from the valley by the mountains, beach cats from the seashore, river cats from the marshy lands near a great lake. Each bound to a common belief in StarClan, each following him to glory and power. Froststar felt a thrumming in his heart as he looked at the mass of warriors under his command.
"OneClan! Today, we make history! Once we were small, alone in the world, squabbling over prey and meager territory that could barely feed our Clans. But this is true no longer!" His words were met by a roar of approval. "Now we are united under a common cause! Now we are OneClan! And, united, we shall bring the light of our new confederacy to yet more Clans." Another cheer went up from the assembled crowd. "Remember this day, for you shall be spoken of in legends to come as the cats that helped unify the Clans and bring light to the world!" The cats were excited to a fever pitch now, springing to their feet with the thrill Froststar brought them.
Froststar smiled. "Now, my brethren, forward! Forward to victory!" The light of the rising sun broke over the crest of the hill, illuminating the pure white of the leader's pelt. As the crowd let out a resounding war cry, Froststar turned and with mighty, powerful strides lead the way onto the restless grassy plain.
I can also put the alleigances here and update them as the story progresses if the readers prefer. Please review!