As for the details, in return for Ukraine giving up the nukes she had at the end of the Cold War, Russia promised to respect Ukraine's territorial integrity and political independence. Then Russia under Putin began fomenting rebellions in the eastern provinces of Ukraine, slipping in men and materiel in a covert slow motion invasion, and suborning Ukrainian politicians through bribery and coercion.
Euromaidan was a Ukrainian popular reaction against a government that had been bribed by Russia to abandon their election promises and adopt pro-Russian policies. Ukraine's populace had been promised and prefers EU membership as offering prosperity, freedom, and democratic government, with NATO membership to protect against Russian aggression.
When Putin invaded Ukraine in full, he expected an easy victory in part because the Russian spy services had bribed and compromised many Ukrainian politicians and civil and military leaders. Instead, the rank and file Ukrainian military and people at large courageously rallied to defend their country.
Russian agents in Ukraine sagely decided to sit on their hands and profess their love for Ukraine. The corrupt Russian security services had pocketed much of the bribe money, thinking that Russia's military was as strong as they claimed to be.
Russia's military and defense officials though had also pocketed much of the money provided to build up the military. The butt of these scams was Putin, of course, who somehow thought that he could steal with both hands and not have his subordinates not do the same.
For now, there are still many Russian agents in Ukraine that remain hidden and capable of wrecking elections, assassinating Zelenskyy, or fomenting a coup. That is why Ukraine does not try to hold a presidential election and pretend they are Switzerland.