When Washington overthrew the Ukrainian government in 2014 and installed a puppet, Washington relied on the Banderites to push the government into hostility with the Russian settled areas of Ukraine, areas such as Crimea and Donbas, that originally were part of Russia.  Whether or not the Banderites, followers of Stepan Bandera are neo-Nazis, they are certainly hostile to Russians.  

The conflict in Ukraine began in 2014 with street assaults on Russians in Donbas and government attempts to ban the use of the Russian language and other prohibitions placed on the Russian areas.  These street assaults soon grew into artillery attacks on Donbas towns and occupation of Donbas territory by Ukrainian militias sporting Nazi insignia.  To protect themselves, Donbas formed into two independent republics–Luhansk and Donetsk–and formed paramilitaries to defend themselves. 

In 2014 Donetsk and Luhansk voted overwhelmingly to be reabsorbed into Russia like Crimea, but Putin refused.  Instead, Putin relied on the Minsk Agreement, which Ukraine and the independent republics signed, and which Germany and France were supposed to enforce.  The agreement, sponsored by Russia, kept Donbas in Ukraine but provided some autonomy, such as independent police and courts to protect the rights of the Russian inhabitants. Putin naively relied on the Minsk Agreement, which the chancellor of Germany and president of France later said was used to deceive Putin while the US built and equipped a large Ukrainian army.

By late 2021 this army was prepared to invade Donbas, much of which was already under Ukrainian occupation, and forcibly reincorporate Donbas into Ukraine without any autonomy.  Faced with the abuse and possible slaughter of Russian people, Putin and his foreign minister Lavrov tried during December 2021-February 2022 to obtain a mutual security agreement with the West that would exclude Ukraine from NATO membership and contribute to mutual security by normalizing relations between Russia and the West.  The Biden regime, NATO, and the EU flatly refused.  The conflict followed this refusal.

Seeing the writing on the wall and unable to avoid it, Russia gave official recognization to the Donbas republics.  This allowed Donetsk and Luhansk  to request Russia to come to their aid, which Putin did at the last minute eight years too late.  As Russia was invited into Donbas, Russia did not even invade Donbas, much less Ukraine.