1)Euromaidan.
It was supported by the USA, involved many far-right and Neo-Nazi militants and resulted in an unconstitutional overthrow of an elected president, but it was also a genuine grassroots popular revolution against a horrendously corrupt dictator that has run his country down into a standard of living that was lower than that in the Ukrainian SSR while building himself a mansion with several golden toilets. After Yanukovich fell, however, the new government quickly proved itself to be vocally anti-Russian, even more corrupt and outright totalitarian, disposing of political opposition via right-wing militants, putting a stranglehold on state media and appointing prominent neo-Nazis to positions of power (
here's a list, you can ignore the commentary and just check the names on wikipedia). Poroshenko's Ukraine is quickly becoming increasingly nationalistic in the worst sense and anti-Russian: famine of the 1932-1933, "Holodomor", is widely advertised and stated to be a genocide of Ukrainians at the hands of Russians (even assuming that the famine was deliberately manmade, which is extremely debatable, the Soviet leadership at that time was multi-national, the official list of Holodomor organisers presented by Ukraine contains only two Russians), historical revisionism runs rampant and Russia is defamed just like the USSR was defamed during the 90s in Russia.
2)Crimean annexation/reunification/secession/referendum.
Crimea was filled with insignia-less Russian soldiers (on a very flimsy legal basis, they were officially the personnel of the Russian naval base in Sevastopol) and a referendum was organised that resulted in Crimea seceding from Ukraine and (re)joining Russia. On one hand, Russia ignored both international law and political agreements by getting Crimea back. On the other hand, ignoring all possible irredentist arguments,
the absolute majority of Crimean population supported the Russian troops, actively wanted to join Russia and believed that the referendum was free and fair. This was most likely due to the openly pro-Russian Crimeans being afraid of the new Ukrainian nationalists in charge of Kyiv, especially since conflicts between Crimeans and the rest of Ukraine were frequent in the past. Since then, Crimea has been wielded politically as a convenient political beatsick for the USA to use on Russia and an official excuse for the sanctions.
3)Donbass rebellion/Ukrainian civil war.
Just like the Crimeans, the Russian-speaking, Russia-supporting people of Donbass were afraid of the new hardline pro-Ukrainian government in Kyiv.
The result was another grassroots movement, this time an armed uprising that began when armed protesters seized control of Donetskaya and Luganskaya oblasts' central government buildings and proclaimed independence from Ukraine. Ukraine's response was to do what Yeltsyn did in Chechnya and send its armies on an "Anti-Terrorist Operation" to crush the rebels with excessive force. As a result, civilian areas of the rebel cities have been indiscriminately shelled by the Ukrainian armed forces, killing many thousands of people and displacing at least two million. Also, so-called "volunteer battalions" that are composed mostly of far-right radicals and neo-Nazis and are, essentially, private armies of the oligarchs that fund them took part in the ATO and became known for many war crimes, including killing civilians and torturing POWs. USA has actively supported Kyiv with funds and non-weapon supplies and also pressured it to continue the ATO on several occasions. The rebels, meanwhile, formed their own militia regiments, which are mostly disorganised and led by constantly squabbling commanders. Russia, for its part, provided supplies and training for the rebels, and on one or two occasions, even troops, although the absolute majority of rebel fighters are locals and most of the rest are "battle tourists". So far, Ukraine hasn't won despite its absolute advantage in men and material due to low morale, widespread corruption and horribly incompetent leadership, as the ATO forces are being commanded by people who have no military training whatsoever. The rebels' command, though, was little better - a nest of vipers, it's most commonly regarded by the rebels themselves as actively detrimental to their war effort. Humanitarian situation in the rebellious Novorossiya territory is catastrophic, especially since Ukrainian forces have started stopping the aid convoys from Russia. Non-rebel Ukrainian territories have not been directly affected by the war so far. People from the shelled territories are growing increasingly bitter and peaceful resolution of the conflict is becoming increasingly distant.