It could be argued that was also Uruguay's case. To sum it up, Uruguayans 'independence heroes' originally intended it to be a province of Argentina when it was under Brazilian control but then Brazil and Argentina agreed to grant Uruguay independence as a neutral country (a buffer state), without any participation of Uruguayans in that decision.

Control of the current territory of Uruguay (historically known as the "Banda Oriental" or 'Eastern band', as it sat on the eastern side of the Uruguay river) had long been a source of contention for the Portuguese and Spanish empires, with the former founding Colonia del Sacramento in 1680 (just 50 km away from then-Spanish Buenos Aires) and the latter taking over and founding Montevideo in 1724.

In early 19th century, when formerly Spanish territories started to gain independence, Spanish-speaking "Banda Oriental" became part of the "United Provinces of the Rio de la Plata", a precursor to Argentina, then it seceded along with other provinces to form the more confederal-minded 'Federal League' (Liga Federal) which defied the more centralist government of the United Provincies in Buenos Aires. By 1821, the Federal League fell and the current territory of Uruguay was annexed by Portugal (or rather the "United Kingdom of Portugal, Brazil and the Algarves") as the "Cisplatina" province. The province was put under Brazilian control when Brazil became independent.

Argentina (the United Provinces of the Río de la Plata) never relinquished its claims on the "Eastern Band" (or "Eastern province", provincia oriental), which would be one of the leading causes to the Cisplatine war between Argentina and Brazil.

On 25th August 1825, a group known as the "33 orientales" (33 easterners, from the 'Eastern band', supported by Argentina) signed what Uruguayans often see as their 'declaratory of independence'. The document consisted of three laws: the independence law (declaring independence from Brazil, Portugal, Spain and 'any other foreign power'), the union law (declaring that the Eastern Band / Cisplatina would return to the United Provinces / Argentina) and the flag law (which stated a flag design which is not the one currently used in Uruguay either). Even though August 25th is officially celebrated as 'Independence Day' in Uruguay, their intent was clearly to reunite the 'Eastern Band' with Argentina.

As Cisplatine war approached an stalemate, Argentina and Brazil reached a peace treaty through British mediation, the 1828 treaty of Montevideo (also known as the 1828 'Preliminary Peace Convention') which, among other things, decided that the territory of Uruguay shouldn't be controlled by either country but rather be granted independence instead (working as a buffer state between Argentina and Brazil). This was wholly negotiated between Argentinians, Brazilians and British mediators, with no representation of would-be-Uruguayans themselves. When the news arrived to Cisplatina they were met at first with certain scepticism and reluctance by some local leaders ("caudillos") but they would ultimately agree.

I'm afraid I cannot think of any English-language sources for this, but Lincoln Maiztegui's "Orientales" is an excellent Spanish-language book series that covers these historical episodes.

Actually, it's a bit iffy to say that Singapore was "expelled" from Malaysia "against their will". This has been a popular way of characterizing the 1965 separation, because it feeds into a dramatic storyline, meshing well narratively with Lee Kuan Yew's tearful press interview and Singapore's subsequent economic comeback story.

In fact, the separation was not a unilateral decision by the Malaysian government, but the product of intense negotiations between Malaysian and Singaporean politicians trying to deal with the ethnic and political divisions within their country. (The two governments actively conspired to keep the UK in the dark over their negotiations, for fear of British intervention over the process.) The Singaporean side was not solidly opposed to separation; in fact, by 1964-1965, Goh Keng Swee (then Minister of Finance for Singapore, and Lee Kuan Yew's principal deputy) had soured on the idea of the "common market" between Malaysia and Singapore, which had originally been envisioned as Singapore's route to economic development. Goh later even claimed credit for persuading the Malaysian authorities to have a clean separation instead of a one-country-two-systems type arrangement.