To be honest, fair and factual:
Russia did not break the treaty first. The move on Crimea occurred long after overt efforts to bring Ukraine into NATO became news.
So there are some different twists on the facts. For example, I've followed an ultra-conservative analyst who was writing about this years ago. That information base goes like this. When Ukraine became recognized as "independent", there were few name changes on the plaques on government office doors. So much so that the "independence" was derided as a hoax. Under the USSR, overtly loyal backers of Moscow held all the relevant government posts, in fact the only "candidates" for elections were approved from Moscow. As an "independent" nation, the same people continued to rule Ukraine.
So I've also followed some analysts who speak from a position supportive of Putin, as well as others, including CFR and other western experts. I had a niece in Kiev, and a friend who was on the task force inspecting compliance with the disarmament treaty who was in Ukraine several times.
It is likely true that western interests have carried intentions to lead the satellite republics of the old USSR into the western camp generally, and Putin likely knew and expected that to be the fact. But the parties all signed the deal.
In the year before Ukraine became a news item, western interests were funding fascist remnants supportive of fascist ideals from the Hitler era. Well, at least according to Russian-supportive sources of that time. Western money, Western media, even Western agents sent into Ukraine from NATO countries were all at work. The ultra-conservative analyst was hooting it up about how it was all a puppet show, a grand little diversion of public sentiments intended to put us into a frame of mind to be supportive of a new war being planned cooperatively by "higher ups" on both sides, sometimes termed a "bowery war" like the Aztecs used to have with their "enemies". According to the history, Aztec royalty and their counterparts from surrounding kingdoms would march their armies out to face each other, and they would assemble their royal asses on a lookout hilltop, both sides' highest elites, together under a nice shady bowery, and proceed with some drinking and other pleasures, and watch the armies at the foot of the hill, cheering impartially for warriors of merit. The prevailing forces would wax and wane, and both sides would retire with a nice take of "prisoners of war", which both sides respectively would induct into their service staffs as slaves. So it has been with the world under the UN governance era, with perhaps the new twist that rather than take slaves, we take technology. And support our military-industrial financiers and corporatists.
But, be that as it may be, there was a "regime change" in Ukraine that installed putative pro-Western government, which however again failed to replace the old Soviet bureaucrats. . . . which had my source still talking puppetry, smoke and mirrors, and brainwashing through posturing and media, on both sides of this issue, more or less advancing the "crisis" as a war threat.
And after the move to induct Ukraine into NATO, contrary to the alleged "treaty", Putin did move to assert control over some areas of Ukraine deemed strategic militarily, or where it could be credible there was public sentiment supportive of Russia.