Some advances (Cybanthropic Merge and Brainwave Disruption) confer the special ability called Total Defense. For a nation with Total Defense, once two hours have passed since a player belonging to that nation has been online, its Hit Points Per Square increase by 50%. This makes it a lot more difficult for attackers to capture the nation’s land while its players are offline. Total Defense deactivates as soon as a player logs into the nation, and becomes obsolete once the nation reaches level 110.
When attacking a nation that has Total Defense active, you will see a blue shield on their combat stat icon in the Battle Display.