The Lone Shadows are a terrorism organisation lead by the Mienfoo Dante. The sole purpose of the group is to cause chaos throughout the Pokéarth and disorder. Originally Dante was the only member, though he recruited stronger Pokémon while he invaded different towns.
The raid on Corakuda was a representation of how much power Dante had got over the years and how he'd rose up higher than the leaders of towns around the Pokéarth. The Lone Shadows' warships came onto the coast and begun flooding the city with soldiers. Despite the amount of soldiers in the area, the player is able to hold them off and take out the warships.