International reasons
The Russian regime has too much to see the light of day, if once Ukraine joins the West, it will certainly be transformed in a democratic way, which will inevitably threaten the survival of the Russian regime, the Ukrainian people in the democratic process of the kind of will be gradually rich and strong, living in the bottom of the Russian people will be attracted by the democracy, the internal conflict in Russia will be aggravated or outbreak, at the same time, the West will certainly threaten the survival of the Russian regime.
The Russians have been in the midst of the war for a long time now, and they are now in the midst of the war for a long time now.
Russia has always wanted to restore the status of the former Soviet Union as a superpower, want to have a stronger influence in the international arena, rowing against the current, not to advance is to retreat, or to develop a strong, or to be democratically extinguished, there is no other way out of the Russian Federation, backwardness of the domestic industry, the people's wealth gap is too large, advanced things (such as computers, systems, and so on) and can not be produced, relying on the sale of natural gas to earn a little money, but also by the Putin slapped the table and transferred most of the money to his supporters implicitly, making the poor poorer and the rich richer.
In this environment, Russia can't let Ukraine join the Western forces in any case, so it keeps supporting pro-Russian forces in Ukraine against those who are close to the Western powers.
Domestic reasons
Ukraine is located in the eastern part of Europe and is the largest country in Europe in terms of territory except for Russia. Ukraine used to be one of the member states of the Soviet Union, and became independent after the collapse of the Soviet Union in 1991. About one-third of the Ukrainian state speaks Russian, and the other two-thirds speak Ukrainian. Russian-speaking Ukrainians have been under Russian control since the mid-17th century, and inwardly prefer to return to Russia, while Ukrainian-speaking Ukrainians have been living under European influence since the 16th century.
Now pro-Russian in Ukraine are ethnic Russians living mainly in eastern Ukraine, these people are the descendants of the Russian colonizers who moved into Ukraine in an organized, planned and large-scale way to change the demographic and ethnic composition of Ukraine when it was first colonized in the Tsarist and Soviet eras, and enjoyed many privileges during the period of Moscow's rule of Ukraine, until after Ukraine's independence when they also did not speak Ukrainian but used Russian, regarded Russia as their motherland, and reincorporating Ukraine into Russia and turning Ukraine into a Russian colony was their ultimate goal, and were not really Ukrainians at all.
The Russian nation, which has historically expanded aggressively into neighboring countries at every opportunity, and the majority of Russians today see Ukraine not only as a sphere of influence that they must control, but also as a part of the territory they have historically lost, and they have always been obsessed with the ambition to reintegrate Ukraine into their own control, or even into the Russian territory.
If these descendants of the Russian colonizers in eastern Ukraine and their agents are allowed to be in power, Ukraine will become a Russian puppet protectorate even if it is not annexed by Russia again, and Ukraine's national independence and national autonomy will become a watery moon and a mirror, not to mention the fact that being controlled by the Russians with their barbaric and tyrannical behavior or being incorporated into Russia as a colony of Moscow will not bring much material and economic benefit to the Ukrainian people, but it will also bring a lot of benefits to the people. Not to mention whether the Russians' brutality and tyranny, control by the Russians or annexation to Russia as a colony of Moscow will bring Ukrainians any material and economic benefits, even if they can, Ukrainians will not give up their freedom and dignity for the sake of a bit of dog food. So the essence of the root cause of the frequent unrest in Ukraine is the struggle to maintain national independence and national autonomy against Russian expansion, which is a matter of life and death of the Ukrainian state and the Ukrainian nation.