At the time fictions like "Russian-backed separatists" were made up to deny the reality: that it was a foreign invasion. Yet all the signs were there: for example, "separatist" leaders like Igor Girkin were citizens of Russia, not Ukraine; OSCE observers found military vehicles containing documentation indicating that the equipment had been maintained in Russia.
European leaders called for "deescalation", "political resolution"; seeing weakness and appeasement in the Minsk agreements, Putin escalated. That's the problem with aggressive leaders like Putin: if you look weak and vulnerable, they will attack you.
Russian leaders see Russia as an empire and regularly say Eurasia should extend from Lisbon to Vladivistok. Putin tries to terrorize us, stating that if we resist it will lead to "World War III" or "nuclear apocalypse". We must not fall for this, or we will gradually lose our freedoms.