I think the eb descriptions try to piece together a story and the rancor trials have a backstory (sort of). Besides that... Not much in the way of lore. It's the people that make KaW what it is.
In the beginning, there was Spragga, and Distance. Spragga, according to legend, appeared small and innocent. Thus, distance hired him as a pet. Together the two built up their lands and brought more into our realm. Distance built mighty Volaries, and majestic COE, but the spragga built only stables. He filled his lands with them, even the highlands. Distance scoffed at spragga, as did the others, but that all ended when spragga unleashed his true form. A horrendous creature, a formless, shifting blob with millions of horse legs and horse heads, all eternally kicking and neighing, rolled into Distance's mighty kingdom and destroyed it in minutes. His gold was gone, his castle reset, buildings all smoldering ruins. All the others who had laughed at spragga stables now screamed in terror and bunkered down in the now legendary Caves of Shadow, released quickly in secret with the cave code. Those armed with the code were safe, but outside they could hear the constant neighing, the sounds of screaming and burning, and overall the sounds of noobs praising their Spraggan overlord. For 68 days and nights, the lucky few huddled in their cave feeding on Kaw_admins dank memes, until finally on the 69th day, when Kaw_creative drew chains on Spragga, did the torment stop. We were saved, finally, but the day will rise again when Kaw_Com, and his shark legions, battle through ZAFT, protectors of the Pit that holds spragga, and free him to once again destroy our lands.
The events have a little lore to them. They all have stories. They also had a big "Farmers Journey" story, which wasn't too bad. Search it on forums.
Well you mentioned spragga, I thought it'd be coolio.. I shall appease the beasts, we will win the day, and the battle Maybe not