From game rules:
Each player is allowed to have one account and nation. Having multiple nations is a bannable violation. There is no limit on the number of nations that can play per network, so long as each nation is owned and controlled by a separate individual. Some restrictions will be imposed automatically on nations on the same network to prevent cheating. Using Alliance Banks to evade trade restrictions imposed on nations on the same network is a bannable offense. Two nations on the same network are allowed to be in the same alliance, but they are not allowed to declare war on the same nation. Failure to follow this rule will result in a nation strike the first time, and a ban the second time.