Most of the Makran Coast from Oman in the 1950’s. This was done peaceably… Pakistan Government threatened to attack Oman directly if Oman did not agree to a sale as attested by Ayub Khan’s diaries
the Princely states of Dir and Bajaur in 1962.
Swat and Bahawalpur, independent states under Pakistani suzerainty in 1970.
Actually, the text of the Treaty makes no mention of the Soviet Union getting control of the territories. According to Wikipedia, that was one of their reasons for not signing.
For what it’s worth, Senegal did at one point want to incorporate the Gambia. They had a kind of confederation (called the Senegambian Confederation, if you can believe) that lasted between 1982 and 1989. Hard to imagine Senegal suddenly wanting to get together again.
A. Gwilliam already mentioned the pseudo-independent homelands in South Africa as an example of a boundary change in Africa. In one case this did lead to a sort of annexation. The four nominally independent homelands were supposed to return to being part of South Africa on 27 April 1994, the date of the first non-racial elections. In three of them this was accepted, but Lucas Mangope, the leader of Bophuthatswana, banned political activity and declared his intent that his “country” remain independent. The Bop police and army went on strike, and Mangope called on, ironically, a right-wing white militia to come in and defend him. To cut a long story short, the situation turned into a huge clusterf**k, and the South African government sent in its army to remove Mangope and install an interim administrator. One could regard that as a South African annexation of an unwilling Bophuthatswana; but of course it was only the Bop government that was opposed to annexation, while the majority of the Bop people were for it.
No territory changed hands, but when mainland China and Taiwan battle over the islands of Matsu and Quemoy in the 1950s-1970s, so many artillery shells were fired that the locals still use the steel to make knives and cleavers.
What does “on paper” mean in this context? The closest thing to an official register that I’m aware of is the UN’s list of non-self governing territories, which seems to accept Spain’s complete withdrawal.
The footnote there says “In 1990, the General Assembly reaffirmed that the question of Western Sahara was a question of decolonization which remained to be completed by the people of Western Sahara.” (Bolding mine)
There are, IMHO, a few ways that can be interpreted, with one of them being “The territory hasn’t been formally decolonised, so until the Saharis vote on the matter, it’s still Spanish territory although Spain says it’s not.”
In other ways, decolonisation has begun, but part of it is still has to be completed. And the part that is still to be completed is not the part of the former colonial power - which is gone - but the part of the indigenous people.
Territory in international law doesn’t work the way that property ownership does in national law. It’s a question of the dual factors of control and recognition. Neither of those factors exists in this case - Spain clearly doesn’t control Western Sahara, nor does it seem that anybody recognises it as de jure sovereign, least of all Spain itself. So I don’t see how it can really be said that it is still part of its territory.