Russia absorbing Crimea will be the first time since 1945 that a country other than Israel has taken over a part of a neighbouring state and formally annexed it, other than colonial outposts. Some people are maybe not appreciating what a break with international norms that is.
A few of those annexations of colonies were a lot more brutal affairs than Crimea: Ogaden, East Timor, Western Sahara. It’s still a very short list. Iraq and Kuwait was very briefly an exception and was supposed to once and for all end that sort of thing (and end history).