The Ukrainian army is not a war trained well disciplined army. Ukraine's army is domestically defensive but could be crushed in days by a real expeditionary army like Russia's ... For instance; the Russian army is experienced in dealing with separatists in the Chechen Republic, NATO forces have experience in Kosovo in civil warfare tactics.

Neither the US army or the Russian army could not effectively control separatists like the Taliban, et. al in Afghanistan. The French and Americans (with allied forces) in Vietnam. The Israeli army in the Israel/Palestinian conflict which is essentially a separatist conflict now, over 40 years. The British army in North Ireland was dealing with separatists for 30 years (1968 - 1998). The American Civil War (1861-1865) in the USA went on for four years it was a separatist war too, albeit a all out war ...

So, why would you expect the Ukrainian army to sort out the separatist issues in weeks?