Which US states would be hardest to invade?

If an army somehow landed in the United States, some states would be far harder to hold than others. Population and military bases matter, but geography decides most of it. These five would be a nightmare.

The ranking

1. Alaska. It covers about 663,000 square miles, more than twice the size of Texas, and most of it has no roads at all. Brutal winters, mountains and tundra mean an invader would struggle just to reach most of the state, let alone control it.
2. Colorado. It has the highest average elevation of any state, at about 6,800 feet. The few highways across the Rockies squeeze through narrow passes and tunnels, so a small defending force could block them while the terrain does the rest.
3. Wyoming. It has the smallest population of any state and sits almost as high as Colorado. Huge distances between towns would stretch any army's supply lines thin.
4. Montana. The fourth-largest state has only about a million people. An army could drive hundreds of miles and still control almost nothing.
5. Florida. It looks easy on a map, but the Everglades and other swamps make natural defensive ground. Add coastline on three sides, dense cities, hurricanes and crushing humidity, and it becomes a logistical mess.

Terrain is the best army

Look at where people have held off far stronger invaders throughout history, from Afghanistan's mountains to Russia's endless winter. The pattern holds: high ground, bad weather and long distances wear down an attacker before a single battle is fought. America just happens to have a lot of all three.

Sources: US Census Bureau; US Geological Survey elevation data; National Park Service; US Army Center of Military History, "The Aleutian Islands" campaign history.