Scotland was "ruled" by Edward Long Shanks, then under Robert the Bruce became free.
In 1707, Scotland opted to join with England.
The group chosen to discus the acts of union were chosen by a pro union Duke of Queensberry, and were mostly pro union.
Another case I remember reading was about Eadric Streona .
He was a traitor for both the English and the Danes.
He joined Knut against the English, then joined the English against the Danes in the battle of Battle of Assandun .
During that battle, he deserted and joined the Danes again, securing their victory.
When England was under Knuts thumb, Knut, who knew the Eadric was not trust-worthy, had him executed.
This example might not be what you are looking for, because Eadric didn't switch sides because of a scene of loyalty or necessity, but rather for monetary and power gain.
Also, Eadric wasn't a king of a country, but rather the Alderman of Mercia, the equivalent of an earl.
(earl came into use after Knut appointed Jarls, but the English couldn't pronounce Jarl, and so said earl.)
On the other hand Mercia was still very much a separate entity, and an earldom was very much a sovereign power
thanks the the decentralizing effect of feudalism.
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A textbook example of this occurred in Zimbabwe/Rhodesia in 1979.
The country had been effectively independent for 14 years.
A whites-only government had unilaterally declared independence from Britain in 1965.
But in December 1979, as part of the deal by which transition to majority rule was to take place, the Rhodesian parliament voted itself out of existence .
Power was handed back to London and an old-style colonial governor (in the considerable shape of Lord Soames) was despatched to Africa to take over.
The flag of British Rhodesia reverted to the Union Flag (with Rhodesian arms) instead of the flags (predominantly the green-white-green tricolor) which had been flown by the de facto independent states of Rhodesia and (briefly) Zimbabwe-Rhodesia.
It was always intended to be a temporary arrangement, to allow for free and fair elections to take place.
The elections were held a few months later and independence was duly celebrated in Zimbabwe in April 1980.
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Bonaire, Sint Eustatius, and Saba are Netherlands Antilles islands which have rejoined the Netherlands following the breakup of the Netherlands Antilles as a country.
The other 3 Antilles islands have opted for nationhood, although still as part of the Kingdom of the Netherlands.
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Some time after the unification of China by Qin, Ren Xiao and Zhao
Tuo were sent to colonise the barbarian region of Nanyue around present day Guangzhou.
Zhao Tuo succeeded Ren Xiao around the time when revolts began to occur against Qin, eventually signalling Nanyue's independence by declaring himself King and raiding surrounding provinces.
When Liu Bang reunited China, the diplomat Lu Jia persuaded Zhao Tuo to submit to Han, although he retained his title of King.
However, after Liu Bang's death, his widow Empress Lü cut off trade in iron goods with Nanyue, as a result of which Zhao Tuo declared himself Emperor of Nanyue, dispatching troops to attack Han and sending bribes to nearby chiefs to encourage them to switch allegiances.
Empress Lü sent troops to attack him but disease led to the failure of the mission.
After Empress Lü's death, Emperor Wen took the throne.
Once more, Lu Jia persuaded Zhao Tuo to submit to Han, renouncing his title of Emperor and returning to being King.
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In 1860 the Dominican Republic, some 15 years after independence and in turmoil, asked to be readmitted to the Spanish Empire .
It seems that debts and the threat of invasion prompted the request, which was readily agreed to by the Spanish.
The relationship quickly broke down and the territory was soon in revolt.
Spain was unable to reassert control and within five years the country was again independent.
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The British colony of Newfoundland became a mostly independent dominion in 1907.
In 1933, facing crushing dept in the Great Depression, Newfoundland seems to have become mostly a British Colony again while ruled by the Commission.
In 1948 the citizens voted in a referendum to become part of Canada instead of continuing under Britain, or regaining independence.
Some wanted to join the United States but Britain and Canada kept that off the ballot.
https://en.wikipedia.org/wiki/History_of_Newfoundland_and_Labrador[1]
Persons more expert on Newfoundland history may want to confirm or deny or clarify my impression that an independent Newfoundland agreed in 1933 to become some sort of British possession again.
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Is there any country(former colony) in the world that fought for/obtained independence and then again tried to join its colonist ruler?  I guess an African country did so.   Can anyone tell me?
Is there any country(former colony) in the world that obtained independence and then again tried to join its colonist ruler?
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<independence><colony>
history.stackexchange.com/questions/2221
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Zimbabwe, islands in the Antilles and the Dominican Republic have all fought for independence before rejoining their old nation. There a few examples of this occuring, including Zimbabwe, the Netherlands Antilles islands and the Dominican Republic. The exact reasons in each case are less clear.
There a few examples of this occuring, including Zimbabwe, the Netherlands Antilles islands and the Dominican Republic. The exact reasons in each case are less clear.