Undefended (adjective)

Not protected by military forces or fortifications.

Origin:

From the prefix un- meaning not and the past participle of the verb defend.

Examples:

1. The enemy easily conquered the undefended village.
2. The undefended coast was vulnerable to attack.
3. The hikers were in danger because they were in an undefended area.
4. The undefended border allowed smugglers of illegal crossing easily.
5. The undefended city was ransacked by the invaders.