The king consolidated the empire into a powerful nation.

Answer: Option D

Consolidated : make (something) physically stronger or more solid.
Divided : split into parts; separated.
Isolated : far away from other places, buildings, or people; remote.
Fragmented : break or cause to break into fragments.
Weakened : make or become weaker in power, resolve, or physical strength.

Antonym of Consolidated is Weakened