It was an invasion of Eastern Ukraine sending in thousands of Russians to instigate conflict then sending in Russian military 'unmarked' troops ie almost exactly like the illegal military occupation of East Timor by Indonesia using militias. Unmarked troops from Russia are militias and worthy of being shot on sight had Ukraine not been so deeply undermined by the infiltration of thousands of Russian separatists over the previous 2 years leading up to the annexation of Crimea which is Ukraine territory these unmarked troops would have all been KIA. Ukraine was not ready then but now Ukraine vow to take it back and that looks to be the case
