I don't know if only Putin is to blame for starting that war. From my point of view, the culprits are Putin together with Zelensky because they were not able to manage their own wills at a pacifist level.
I get your point, but the war is still hugely in the hands of Putin because the USA said he was going to invade and he denied it up to the night before the invasion. Most of the Russian soldiers had no idea of what they were going to do until the last minute. Also Zelensky and many other Western leaders didn't believe Putin was truly going to invade Ukraine and that's why at the beginning of the war Ukraine's forces were caught unaware and not defending their capital but rather the hotbeds in the south