Thats what the Crimean people wanted, they asked Russia to help them after the illegal coup in Kiev and held a referendum to return to Russia. It is a majority Russian speaking area, Russia has military bases there, and they are otherwise landlocked on that side of Russia.

You might ask, why does the U.S. need Puerto Rico, or Guam.

This news story may be of interest. Possibly the only Israeli news source that is not in lock step with the right-wing government.

Russia took advantage of the unrest to reclaim what many believe to to be theirs. There are those who support it, and there are those that are not happy with the result. There are economic and other benifits that Russia gains from it.

The same reason why you need your leg or arm. Crimea has been Russian for centuries. There are Russian people living there, whose Russian ancestors died in many wars fighting for their Motherland.

Learn some history.

It is the only yearlong, icefree, warm water. Russian, port. It houses the Russian Black Sea Fleet. It is the last strategic place to park a surface combatant throughout the winter.