Starting in 1999 NATO repeatedly violates promise to Russia to not expand eastward.
2001 US unilaterally pulls out of Anti-Ballistic Missile Treaty and starts placing nuclear capable missiles closer and closer to Russia (such as Aegis systems in Romania ).
2008 US declares intention to integrate Ukraine and Georgia into NATO after Putin warned in 2007 that Russia considers the incessant NATO expansion a threat to peace and stability in Europe.
2014 US and EU orchestrate Maidan coup in Kiev using US funded NGOs, violent Neonazi groups, and snipers shooting into the crowd to overthrow the elected government of Ukraine.
The reason for this overthrow is the attempt by the Yanukovich government to chart a neutral course between NATO and Russia, and its refusal to sign a very bad deal with the EU that would have required Ukraine to destroy its economic ties to Russia on which Ukraine's economy still very much depended.
(This was actually the second time that the US orchestrated a regime change in Ukraine, having previously done so once already in 2004, but that one did not stick; they ran the same script in Georgia 2003 installing an anti-Russia proxy regime that started the 2008 war )
The newly installed ultra-nationalist regime which includes notorious Banderite Nazi parties "Right Sector" and "Svoboda", its leaders handpicked by the US state department, immediately begins passing laws to marginalize and exclude the Russian language, suppress Russian media and pro-Russian political parties, ban Russian books and rewrite history according to Banderite Nazi narratives.
2014 Anti-Maidan protests erupt across predominantly ethnic Russian Eastern Ukraine. The Nazi massacre of anti-Maidan protesters in Odessa and other similar massacres across Eastern Ukraine lead to armed uprisings, mass defections from the Ukrainian army in the Donbass and formation of volunteer militias to defend the people of Eastern Ukraine from Kiev's Neonazi thugs.
Crimeans, fearing similar treatment by the new Kiev regime - a regime which now glorifies and elevates as national heroes groups and figures who committed unspeakable atrocities during and after WWII in Ukraine - overwhelmingly vote in a referendum to secede from Ukraine and rejoin Russia (of which they had been a part until Khrushchev transfered Crimea to Ukraine in 1954 for administrative reasons).
(Crimea had previously held various votes for autonomy/independence between 1991-1994, but these eventually ended when the Kiev government, with Yeltsin's Russia's tacit approval, decided to arrest and dissolve the popularly elected Crimean government that was about to hold a referendum to re-join Russia in 1994.)
2014-2022 Kiev wages a brutal war against the Donbass for eight years.
2014/15 Minsk Agreements signed to negotiate ceasefire between Kiev and rebel forces under the condition of granting autonomy and rights to the Donbass, with Russia and the Europeans as guarantors and supported unanimously by a UN resolution. These are later revealed as a sham used to trick Russia while preparing for war.
Ukraine, with the help of NATO, proceeds to build up the second biggest army in Europe after Russia. Kiev never implements the Minsk Agreements and openly brags about never intending to do so.
2019 US unilaterally pulls out of Intermediate Nuclear Forces Treaty
2021 Ukraine threatens to pursue acquiring nuclear weapons if not allowed into NATO. Similar belligerent rhetoric from Zelensky at 2022 Munich security summit.
Dec 2021 the US refuses to even engage with the Russian draft treaty proposal for a new security architecture in Europe that would guarantee peace in Ukraine.
Ukraine begins in 2021 to mass troops for an invasion of the Donbass. Early 2022 Kiev regime forces launch massive preparatory artillery shelling ( confirmed by pro-Western OSCE ) for invasion of Donbass in violation of Minsk agreement ceasefire.
One week later, Russia recognizes the Donetsk and Lugansk republics (following the UN recognized principle of self-determination that the US and EU themselves previously applied to justify the legality of taking Kosovo away from Serbia), accepts their request for collective self-defense according to article 51 of the UN charter and launches a Special Military Operation to demilitarize and denazify Ukraine.
