The people of the Previous Era feared Herrschers and Honkai to an extraordinary degree, largely because two continents had been devastated, even destroyed, by Herrschers in succession.
The first was Australia. Fu Hua's captain, Himeko, became a Herrscher during the Seventh Honkai and burned all of Australia to ash. However, judging from the background chapter on Fu Hua becoming a Fusion Warrior, Australia underwent a certain degree of reconstruction.
The destruction of Mu Continent pushed the people of the Previous Era's fear of Honkai to its peak. During the Ninth Honkai, the Herrscher of Earth created a Pseudo-Black Hole and destroyed Mu Continent—the most prosperous place on the entire planet.
Note: it was destroyed, not swallowed. The Herrscher of Earth's power was nowhere near enough to create a black hole large enough to swallow an entire continent.
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