Assignment of Crimea to Ukraine was an internal assignment within the USSR, from the Russian SSR (or whatever) to the Ukrainian SSR. The USSR is kind of a weird beast - it was nominally a union of equal republics, but it was dominated by the Russians. In a certain sense, the transfer within the context of the USSR wasn't important to Russians at all, since it was still part of the USSR and Russians ran the USSR - didn't matter THAT much that it was part of Ukraine (though there still werevarious Russian objections to the transfer throughout the Soviet into the Post-Soviet era), at least from an geopolitical standpoint.

When the USSR dissolved... well, it was definitely a period of chaos. As for why wait till 2014? I have no answer for that.

There's no clean US analogy, since the US doesn't have a singular state that completely dominates its political landscape.