If Nato didn't exist, Western Europe could focus on building defending forces against Russia rather than spending their defense budget on expeditionary forces that need to tag along on American-led adventures like Iraq or Afghanistan.

How would they effectively do that though without the cover of the US nuclear umbrella?

You really think Germany couldn’t build all the nuclear weapons they wanted to?

I do think that - how would you go about testing them with a nuclear test-ban treaty in place?

* Assuming that Germany remains responsible and doesn’t go NK route. Maybe that’s not reasonable.

* also assume we are talking about modern thermonuclear weapons