“Any planning for a war [with the U.K.] would need very careful diplomatic preparation these days, much more than in 1982. Back then, Argentina was following a long line of actions that held that the “1945 line” did not hold for European overseas territories. Morocco could invade the Spanish Sahara, India could fight a war with Portugal for Goa, Indonesia could march into East Timor and Dutch New Guinea. Given this history, it was not (completely) crazy for the Argentine generals to think that the world would accept their victory. (And to be honest, I suspect that they were right: if they had won, las Malvinas hubieran sido argentinas.) But that is not the case today, even though plenty of countries support the Argentine claim [to the Malvinas].”
In short, there has been a remarkably effective taboo on unilateral annexations unless they involved European overseas territory. There is only one real exception: Israel after 1967. (Wikipedia adds Sikkim, which India annexed in 1975, but Sikkim had not been an independent state.)
How do we know that the taboo is effective? A case can be made that the taboo limited the extent of interstate wars in Latin America. For example, El Salvador and Honduras fought the Soccer War in 1969 over the status of Salvadoran settlers in Honduras. Since annexing the area settled by Salvadorans was not a possible outcome given the taboo, the OAS (and behind it, the United States) had the leverage to force Salvadoran troops to withdraw. In another example, Peru and Ecuador fought the Cenepa War in 1995. Neither side could reasonably expect to gain or lose any territory outside the disputed region, which made Peru more willing to accept a limited Ecuadorean victory even when Peru had military superiority. (See pages 2 and 3 at the link.) In short, one might believe that the taboo kept both wars from spiralling into protracted total conflicts.
OK ... but the taboo did nothing at all to stop Israel from annexing some border regions. Nor did it prevent the Eritrean-Ethiopian War from turning into a protracted total conflict. Similarly, Paul Collier made arguments that Africa might in theory be better off if governments feared that their states might be forcibly absorbed by neighboring states — but he rejected the implications of that idea by arguing that the lack of interstate conquest was overdetermined: the international taboo was just one of many obstacles to a would-be empire builder in modern Africa. (See pp. 184-85 of Wars, Guns, and Votes.) Considering those examples, perhaps other factors were at work in keeping Latin American wars from spiralling out of control.
The debate matters. If the taboo is key, then Putin’s actions matter beyond near-abroad of the Russian Federation. Successful expansion opens the door to similar actions all over the planet.
But if the taboo on conquest is just a reflection of some other deeper cause, then current Russian actions have implications only for future disputes that involve Russia. Interstate relations between other countries won’t change. David Weman is correct that this will be the only successful non-colonial annexation outside Israel, but maybe that does not matter.
So which is it? Does precedent matter? Will we see territorial aggrandizement that would not have happened absent current Russian actions?