Any cross border troop movements are a violation of sovereignty  States are allowed to take measures for “self-defence if an armed attack occurs”. [1] The movement of troops across the international border from Russia into Ukraine, and from the Russian base in Sevastopol clearly is a violation of sovereignty and Ukraine if it wishes has every right to use force to defend itself even if the Russians don’t fire first. [2]  [1] United Nations, ‘Article 51’, 1945  [2] Deeks, 2014