Disannex usually refers to the removal of land or territory from a legal authority usually removing it to be placed under a different legal authority.

In this case the author is using the term "disannex" to mean a removal of power, or some power, or authority from the king. The power would then be given to the people over whom he is ruling.

The earlier:

" Kings usually have to be trimmed, and it is revolution that does the shearing."

is another way of expressing the similar thought.




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Note added at 16 mins (2010-02-03 12:50:38 GMT)
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from the New York Times, April 12, 1919

"The Walloons of Prussia, feeling great anxiety on account of the news lately published in the press, earnestly request you to decide for the pure and simple annexation of all the Walloon districts of Prussia."

http://query.nytimes.com/gst/abstract.html?res=9F01EFD81238E...

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Note added at 19 mins (2010-02-03 12:54:00 GMT)
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Here's a lively article which gives more of sense of the word.

"In three hours, the aldermen also:

Approved a settlement with Roanoke that releases about 100 acres of Perot land to that city. Roanoke's lawsuit contested about 60 acres of the developer's land that Roanoke contended Westlake illegally annexed. The aldermen could not say how much land was released or why the released property went beyond Roanoke's original demand.
Dumped a franchise agreement with the Lake Turner Municipal Utility Districts hashed out in the 1980's with Nelson Bunker Hunt.
Appointed and swore in White as mayor, whose land they voted to eliminate from the town a short time later.
Authorized payment of the town attorney, although they did know what he would be paid.
Several times, angry outbursts from the crowd interrupted the session.

"Did you take a bribe?" one man demanded.

Another challenged White, "Who elected you?"

Stagecoach Hills resident Jack Walton demanded to know how the aldermen could move to dismantle the town when most residents oppose such a move.

"How does this fulfill your oath to Westlake?" Walton said.

The crown cheered when the board voted to disannex Oien's land. At times, some snickered at the aldermen."

Fort Worth Star-Telegram
Published: May 3, 1997

http://www.westlake-tx.org/history/Star-Telegram/050397.htm

Hope this helps.