You may be looking for the Republic of Acorn, which succeeded the Kingdom of Acorn.

The Kingdom of Acorn is the largest of the free Mobian kingdoms on Mobius, and the last effective bastion of freedom and resistance for those fleeing the Eggman Empire. The Kingdom has endured for hundreds of years, surviving the Great War, Dr. Ivo Robotnik's coup d'état, the destruction of Mobotropolis, the Destruction of Knothole and all-out-war with Dr. Eggman. Its current capital is New Mobotropolis and its rulers are the members of the House of Acorn; its King currently being Elias Acorn, and the people-elected Acorn Council, the latter having been newly formed due to the efforts of the revolution started by Royal Army General Amadeus Prower, which effectively turned the Kingdom into the Republic of Acorn.

History

Foundations

The Kingdom of Acorn formed under Alexander Acorn early in Mobius' history, after the insightful Mobian conceived of combining the talents of all Mobius' inhabitants for the betterment of all. Virtually all the intelligent species on Mobius agreed, the notable exceptions being the Echidnas-who were the most advanced race of Mobius and feared that sharing their knowledge would harm the other races-and the Overlanders-whose violent tendencies didn't sit well with the peaceful Mobians. Because of his inspired idea, the new nation was named the Kingdom of Acorn after Alexander's family, and Alexander himself was made the first king. The kingdom remained at peace through his reign and that of Theodore Acorn though the his reign would be stained with the death of his son Emerson Acorn due to a mishap involving the Overlander Paladin, leading to the Kingdom's ban on guns. (StH: #71, #72, #148 KtE: #12)

The Great War Years

During the great wars 5 years, King Max was a that time the current leader. He and the kingdom tried the best they could keeping the invaders away, but he and the royal army were helpless. By 3220 the kingdoms enemy had already began a siege that would last until the mobians surrendered. The kingdoms population was fairly safe, but Max knew that it wouldn't last. Many mobians tried to stop the repeatedly advancing troops and sometimes with little sucsess. However it was not enough and the kingdom would soon fell. Things changed however when Julian Kintobor (a.k.a  Dr Robotnik) an scientist from Megaopolis fled from prison in which he had been put by his brother Colin Kintobor, but somehow Julian escaped captivity and fled. He was then found by Charles and Jules who brought him before Max. Julian convinced them the only way they could get rid of his people, was if they agreed to that Julian could produce weapons of mass destruction, and let him be a part of the battle tactics. Because of this, the Overlanders siege was drawn back- as Julian's tactics and weapons, were a big part of the thing that made them retreat- and things started to look brighter for the kingdom. Soon with Julians aid all of the Overlanders military was destroyed and finally after 5 gruesome years the kingdom had won. However so shortly there after Julian renamed himself Dr Ivo Robotnik began a coup and seized controll of Mobotropolis. The kingdom fell into disarray because of that. Only a handful of the kingdoms population escaped into Knothole village.

The Rule of King Max

Dismantling

Restoration

Kingdom of Knothole

The Kingdom of Knothole was the reformed kingdom created after Robo Robotnik came to Mobius Prime and captured the rechristened Mobotropolis. Having had Mobotropolis' citizens all flee to the safety of Knothole and realizing it would be near impossible to retake Mobotropolis from Robo Robotnik, King Maximillian Acorn announced the formation of the Kingdom of Knothole to act as a safe haven for those opposed to the tyranny of Robo Robotnik. (StH: #75, #76, #78)

Following Sonic the Hedgehog's disappearance and presumed death after the Xorda's attack on Mobius, the newly created Eggman Empire declared war on the Kingdom of Knothole and the Republic of Station Square. (StH: #125, #130)

The Kingdom of Knothole was completely destroyed during the Destruction of Knothole by the Eggman Empire's Egg Fleet. However, its citizens were rescued shortly thereafter and moved to New Mobotropolis, which became the new capital and home of the Kingdom of Acorn. (StH: #175, #176, #177)

Reform

See: Republic of Acorn

Following Knothole's Destruction at the hands of the Eggman Empire, Amadeus Prower became disappointed in the Kingdom of Acorn failing in its war with Dr. Eggman, while the Freedom Fighters appear to be the ones making real progress in defeating him. Deciding it was time for political change, the Prowers began to conspire to have the Acorns removed from power and institute a democracy. (StH: #175, #177)

Amadeus gave a speech which allowed him to gain the support of half of New Mobotropolis. However, his public speech also resulted in him being incarcerated. When Elias confronted him about his actions, Amadeus was quick to point out how the kingdom had been faltering in their war against Eggman, adding in how under the Kingdom of Acorn, they lost their original home (Mobotropolis), and then Knothole, and how living on Argentium showed him what a government by and for the people could truly do. Amadeus's words cause Elias to regain his old doubts about his ability to rule over his people. Later that day though, Maximillian Acorn comes to Elias, assuring him that the Acorn family has ruled for a long time, and is to stay that way. That night, Miles and Rosemary broke Amadeus out of prison, intending to obtain their demands by force. As they tried to escape, Sonic came in and tried to stop them. Despite his own opinion to the contrary, Tails sided with his parents against Sonic, battling him while Amadeus and Rosemary headed to the palace. (StH: #178)

Once there, Amadeus and Rosemary confronted Elias, demanding that he step down as king and meet their demands. However, Elias, fueled by his father's words, refused, leading him to duel Amadeus for the fate of the kingdom. Their duel was ultimately and mercifully ended when Princess Sally intervened and reprimanded them both for instigating a civil war. Realizing she was right, Elias and Amadeus made up and, together, reworked the Kingdom of Acorn into the Republic of Acorn, where Elias retained his position as king, but had the help of six other people elected by the people of the city as the Council of Acorn. Maximillion Acorn was the only person who wasn't pleased with this change, as he refused to speak to Elias after the news of the kingdom's reformation became public. (StH: #179)

Background Information