NATO appears to me like a gate build in a place where there is no fence at all. With USSR dissolved, and cold war 1 ended, the nail was gone. So it was natural to expect the hammer to go as well. But the hammer remained! With the hammer in hand, of course, everything begun to look like a nail. This mistake would lead to cold war 2!
In a nutshell, NATO is a unity of nations having a common fear. These nations actually donnot love each other at all! They need an outside enemy to remain united. Without an enemy, the unity is in jeopardy. So the end of cold war 1 and USSR was actually a bittersweet experience. Just how can Europe stay together without an enemy? Will they not rivert to the WW1 and WW2 mentality?
Or perhaps that is just a U.S. exaggeration! NATO might be just an excuse to maintaine U.S.'s hagemony. Actually U.S. donnot respect Europe at all! To U.S. Europe is an immoral and irresponsible region that absolutely requires U.S. itself plus an enemy for it to stay together! There seems to be some truth in this, thanks to Trump's extraordinary leadership. He revealed that Europe's unity is just a profound illusions! It is like the way the spokes of a bicycle appears united but only because they are all connected to the same axle. It the case of US-Europe connection, it is for pure convenience. Each nation needs goodies from the fat brother across the Atlantic, beginning from the so called 'Marshall's Plan'. So in this way, US black mails them into its own so called 'sphere of influence'. But US cannot do this forever, especially as China rises economically!
This NATO's persistence despite the fact that the reason for its creation is long gone is the main reason we now have the mess in Ukraine. The problem is that NATO had to justify its indefinite existence by creating ever new fears, once USSR was gone. So, for instance, they bombed Serbia. So they moved from such a massive 'nail' as USSR into a microscopic Serbia. So even though it is defined as though 'defensive', it is actually an aggressive mounster, or so must it turn to be, if it desperately needs an enemy to justify its existence!