Who would have though that our dear Jens Stoltenberg is a Putin apologist; quote:
“The background was that President Putin declared in the autumn of 2021, and actually sent a draft treaty that they wanted NATO to sign, to promise no more NATO enlargement. That was what he sent us. And was a pre-condition to not invade Ukraine. Of course, we didn't sign that.
The opposite happened. He wanted us to sign that promise, never to enlarge NATO. He wanted us to remove our military infrastructure in all Allies that have joined NATO since 1997, meaning half of NATO, all the Central and Eastern Europe, we should remove NATO from that part of our Alliance, introducing some kind of B, or second-class membership. We rejected that.
So, he went to war to prevent NATO, more NATO, close to his borders. He has got the exact opposite.”
It's not controversial to say that Putin doesn't want NATO enlargement, or that preventing it is one of his key goals from invading Ukraine. But I don't think it's reasonable to interpret that statement as Stoltenberg saying that wanting to prevent NATO expansion constitutes a legitimate casus belli for invading Ukraine.
Understanding the motivations of people like Putin is important, even if those motivations aren't morally acceptable.
I do think the author of that article (intentionally?) misses the point though, and arguably is an apologist - it being a motivation doesn't mean that without NATO enlargement Ukraine wouldn't have been invaded, Putin has had overt imperialist ambitions toward Ukraine, which NATO membership would have prevented him executing. Therefore NATO expansion was less a cause of the war, than it was a push for him to start the war earlier before Ukraine was within the protection of NATO.