I think it’s not occupied land as in occupied by force against the will of the inhabitants. The majority of people of Crimea participated in the referendum of which one option was to join the Russian Federation and this choice got the most votes. There are conflicts in international law about “Self-determination versus territorial integrity”[0] which contradict each other like the people of a region want self-determination while the state says it’s illegal. Sometimes it doesn’t work like in Catalonia, sometimes it works like in Kosovo or in a little bit more distant time when a referendum was held to make Hawaii the 50th state after the US annexed it.

0. https://en.m.wikipedia.org/wiki/Self-determination