Russia hasn’t been blameless, but the U.S. has been most responsible for starting the war. From Ted Snider at libertarianinstitute.org:
Though they are being fought in the confusion of a single catastrophic conflict, there are four closely related, but distinct, wars being fought in Ukraine. The first is the war within Ukraine. The second is the war between Russia and Ukraine. The third is the proxy war between NATO and Russia. And the fourth is the direct war between the United States and Russia. Deconstructing this single conflict into its four real wars may be necessary to understand the issues that must be resolved if a negotiated settlement is to be possible.
The latent domestic problems that have been ripped open by this war are not new. They are the torn fabric of the Ukrainian nation. They go back long before the war, and the war will not be safely resolved before they too are finally resolved.
Ukraine has always been a nation divided: northwestern and central Ukraine, which had once been part of the Polish-Lithuanian Commonwealth and then the Austro-Hungarian Empire, have always faced west to Europe; the southeast, long part of the Russian Empire, has always faced east to Russia. Historically, western Ukraine has voted for presidential candidates with European-oriented policies, and eastern Ukraine has voted for presidents with Russian-oriented policies. It is a national tug-of-war that always risked ripping the country in two.