It's not an argument, it is well documented fact. A cursory reading with any detail of the 2014 crisis will mention this. Russia has it's only warm water port i

It's not an argument, it is well documented fact. A cursory reading with any detail of the 2014 crisis will mention this. Russia has it's only warm water port in Crimea as per an agreement between Russia and Ukraine upon Ukraine's independence from the USSR. Ukraine joining NATO means Russia must withdraw from that port. This is militarily not an option for Russia, so you get the annexation of Crimea.