Mykolaiv and Odessa are very important for Russia. If they are under Russian control, this will allow a land route with another self-proclaimed pro-Russian republic of Transnistria, which is part of the Republic of Moldova.
There are Russian peacekeepers (1,500 people) in Transnistria after the war in the early 1990s. There is a limited Russian military contingent guarding Europe's largest Cold War-era weapons cache, located near the Transnistrian village of Kolbasna. There are about 20,000 tons of ammunition in the Kolbasna military depot and it is guarded by a task force of Russian troops. Moldova has repeatedly stated that the Russian military presence in the region must be put to an end. Despite the tension, however, the conflict has been "frozen" for decades and there has not been a single serious incident so far.