You are correct that it had seemed that the world realized that the kind of war we are seeing in Ukraine should have been left in the 20th century.
However, you also forget some of the things we learned in the 20th century. Giving Putin what he wants would only allow him to want more. Also, the last time Russia took over Ukraine Stalin killed millions of people and caused millions of others to starve to death.
Should we allow Trump and his Republicans to get everything they want just to avoid conflict? Bullies are bullies. Racists are racists. They need to be defeated and driven out of power or else they destroy everyone.