Russia wants to protect the ethnic Russians from oppression and also wants to protect its borders, ports and influence that they had under the old Ukrainian government. The EU and the Ukrainians in the east fear that the Russians want to expand and take over the whole Ukraine and become a threat to Europe again.
It is essentially a federalist/nationalist crisis. Eastern wants to remain an autonomous part of Ukraine if possible. If not, they want to secede and join the Russian Federation. The US, EU and Ukrainians in the east want the whole country. A strong pro-EU national Ukrainian government regardless of what Ukrainians in the east want.
Most of the energy, natural resources and industry are in the east too. The west has little, is bankrupt and would be a burden to whoever has it. I doubt Russia even wants it. The EU doesnt want the burden of it unless the east comes along too.
Excellent summary, FreeInWV. Brussels and Washington are trying to resurrect Cold War tensions to drum up support for a distant civil war that is none of our business. Ukraine is a basket case as a single entity, and will likely split between east and west at the Dnieper River. West Ukraine will naturally align with Poland, and East Ukraine with Russia. That looks like the most stable arrangement.
The pronouncements from Right-Sector/Svoboda about getting rid of Russian language and culture in Ukraine, right after the coup, didn’t help matters.