An invasion is defined as 'an instance of invading a country or region with an armed force.' Ukraine has been an indendent country since the signing of the Belovezh Accords in 1991, that dissolved the Soviet Union. The news about the that the Russian president has recognised the independence of two Russian-controlled territories in east Ukraine, that call themselves the Donetsk and Luhansk People’s Republics, and the subsequent incurssion of his military forces on this region of Ukraine, fits the definition of an invasion.
Diplomacy is always the preferred option to avoid a military conflict, but I feel bad for my Ukranian friends, because it seems that the conflict is already there :/, and the world should act accordingly.