Which are most likely to be threats? The Shadows and the Vorlon both have ships capable of rendering a planet uninhabitable. The Centauri have mass drivers for planetary bombardment. The Minbari and the Earth Alliance have the same capability. The Minbari were on the verge of destroying Earth fifteen years ago - in my time, at least - before they surrendered at the Battle of the Line. One ship from that battle, without the Grey Council to give them orders otherwise, could do immense damage. The Earth Alliance under President Clarke is dangerous and unstable which is why the Resistance was formed. It's difficult to predict what a ship's captain might do if they were to find themselves here. They also possess hybrid Shadow tech. The Centauri were expanding rapidly until very recently. The mass drivers they used have been banned by most treaties.