The first signs of division within the Ukrainian society appeared in the 1990s, when Crimea unsuccessfully tried to secede. The so-called "Orange Revolution" of 2004 revealed the cracks in the seemingly united Ukrainian nation - it suddenly turned out that the West and the East have completely opposite political values, and to make matters worse, they despise each other for it. After Euromaidan, the animosity between the two parts of the country became absolutely clear. Even if there was no Putin and no Crimea, a country where one part of the country thinks that the other one is either subhuman cattle or Nazis wouldn't stay in peace for too long.
Look, who are the combatants:
a) Some ideological local pro-Russians.
b) Pro-Russians from all Ukraine who went there instead of triying to do some
c) Local criminals who enjoy the power of an assault rifle in their hands
d) Para-military Russian cossacks units
e) Various Russian mercs making money(Most of which are North Caucasians)
f) Russian soldiers
If that was a civil war in a divided society then we would see hundreds of thousands locals taking arms. I think Putin hoped for that, but that never happened. He failed to ignite a civil war in Ukraine even with all that poured gasoline.
Are there ideological division in Ukraine? Sure. And it is somewhat dependent on geography. That isn't a ground for a civil war. Look at Scotland. They have society divided over the independence issue. It is somewhat dependent on geography, too. But Scottish nation is nowhere close to starting a civil war. It is same for Ukraine.