Singapore was merged with Malaysia in 1963. Singapore has a much higher ethnic Chinese population and ethnic Chinese politicians headed by Lee Kuan Yew were concerned over special privileges to the Malays guaranteed under Article 153 of the Constitution of Malaysia. In addition many ethnic Chinese were suspected of aiding communism and there were many race riots. Finally the parliament voted 126–0 in favor of expelling Singapore.

Lee later wrote in his memoir that he has always been an advocate of unifying with Malaysia because they fought against the common goal of independence from British rule, he was very heartbroken when he had to be the one announcing the independence.

(In the middle of translating a passage from Lee's memoir)

"Some countries were independent to begin with, other countries won their independence, Singapore's independence was forced upon her. 45 British colonies colorfully celebrated their independence from British rule, but for Singapore Aug. 9th 1965 is not a day to celebrate. We have never fought for the independence of Singapore. In the less than 3 past year we convinced 70% of Singaporean voters to vote yes, agreeing to merge with Malaysia. We have said again and again, an independent Singapore cannot survive. Now letting Singapore survive became an impossibly difficult task. How can we let immigrants from China, India, Malaysia, Indonesia, using multiple languages to form one country?

Singapore is a tiny island, the area is only 214 square miles when the tide is low. It is the heart of British Southeast Asia so it became prosperous. After separation from Malaysia, it became a heart without a body. Within our 2 million people, 75% are ethnic Chinese. But we are insignificant among more than a billion Malay and Indonesian Muslims and their 30,000 islands. Singapore is a Chinese island in the sea of Malay. How do we survive in such a hostile environment?

At the same time, not only the export business we have come to rely on since 1819 difficult to predict, but with the disappearance of the British Empire Singapore's war contribution has disappeared as well. 20% of Singapore's GDP used to come from British Defense Department. The British military directly provided jobs for 30,000 people and secondarily employed 10.000 servants. In addition they provided jobs for tailors, business owners, service personnel, etc. They have provided employment for 10% of our workforce. At this time we had severe housing shortage after years of war. In addition unions and Chinese students' radical activities have left a bad name for foreign investors.

一些國家原本就獨立，一些國家爭取到獨立，新加坡的獨立卻是強加在它頭上的。45個英國殖民地舉行了色彩濱紛的典禮，為主權正式由英帝國移交給當地人的政府而慶祝一番。對新加坡來說，1965年8月9日不是什么值得慶祝的日子。我們從沒爭取新加坡獨立。在這之前不到三年的時間里，我們說服了新加坡70％的選民在全民投票中投贊成票，贊成同馬來亞合并。我們說過，一個獨立的新加坡根本無法生存下去。現在，讓新加坡生存下去卻成了吃力不討好的任務。我們如何才能使一批來自中國、印度、馬來西亞、印尼和亞洲其他地區，使用多种語言的移民形成一個國家呢？ 新加坡是個小島，退潮時，面積只有214平方英里。它是英帝國在東南亞的心髒地帶，所以繁榮發展起來。隨著新馬分家，它變成了一個沒有軀体的心髒。在我們的 200万人口當中．75％是華人。在居住著1億多馬來印尼穆斯林的3万個島嶼的群島里，我們的華族人口簡直微不足道。新加坡是馬來海洋中的一個華人島嶼。我們在這樣一個敵對的環境里如何謀求生存呢？ 這期間，不但新加坡自1819年開埠以來所依賴的轉口貿易前途難卜，隨著英帝國的瓦解，新加坡維系英帝國方面的戰略价值也跟著消失。英國在新加坡的防務開支占新加坡國內生產總值的20％左右。英國軍部直接給3万名工人提供職業，也間接雇用另外l万名家庭佣人。除此以外，還有應英國軍人需要而產生的裁縫師、店主、酒吧餐館的員工。他們的存在給超過10％的勞動力創造了就業机會。而且這一時期房屋匱缺情況尤其嚴重，經過戰爭歲月的破坏，沒有足夠的房屋可以滿足需求。另外職工會和華校生的激進行為，使新加坡在世界投資者心目中留下不好的名聲。

Beyond Singapore, which is a pretty unique example, there's a region between Sudan and Egypt that neither claim called Bir Tawil. One could think it was "kicked out" of both countries, because they both wanted to claim more fertile and important Hala'ib Triangle region so Egypt uses a 1899 border that includes the Hala'ib area in Egypt and Sudan uses an 1902 border than includes Hala'ib in Sudan. Bir Tawil is not so much kicked out as repudiated by both sides.

I'm not sure that the Roman Empire would fall under your definition of a "nation-state," but as it's my area of interest, the first thought I had in relation to your question was the Roman withdrawal from Dacia (modern-day Romania and Serbia) in the 270s AD. Trajan fought a series of wars to bring Dacia into the Roman fold in the early 2^nd century AD. However, by the time Aurelian rose to power in 270, it had become a major headache for the Romans -- Dacia lacked a natural boundary conducive to defense (such as the Rhine in Germania or the Danube to the south), and repeated barbarian incursions proved to be a drain on Rome's military resources. Aurelian decided to cut his losses and pulled Roman assets back south across the Danube into Moesia, a part of which he then renamed "Dacia Aureliana."