Yes, the Euro's need the U.S. for their common defense. This is a well known fact. A little thank you to the the U.S. taxpayer would be nice
The whole point of the NATO international alliance is to provide for "
the collective defence" of each member state should it be attacked. It was formed to deter Russian (then Soviet) aggression away from it's member states. That NATO Article 5 is exactly what gives it the strength to be the deterance that it is. It is why NATO exists.
That is exactly why Putin hates it so much and wants to see it's collapse. "You can't just walk in and attack one of us, else you'll have to deal with
all of us".
Role of NATO
Because of the great deterrent force that NATO is, it's only ever had to invoke that Article 5 one time. That was by the US after 9/11. Every single nation nation and 33 others (amongst them Ukraine who had 14 KIA) showed up to fight and die alongside them. Every. Single. One. None asked for "thanks" and none asked for a single dime back for honouring the agreement that they had signed and committed to uphold.
NATO spending
Member Nations' military budget spending is considered their contribution to the NATO funding. There is no minimum required by the signed agreement, but in
2014 directly as a result of Russia's invasion into Ukraine, nations have committed to try to attain 2% of their GDP (not enough IMO) towards their nations' military spending. That would be 2% of taxes per each and every taxpaying citizen in each member nation. There are nations that actually contribute more than the US per citizen taxes to annual military spending (Poland amongst them). Aiming for 4%. Trump has called for 5% GDP contributions from all members per citizen (that would mean the US would have to contribute another 500 billion BTW - see last link in this response).
Canada certainly lags but we are now considering counting "non-hard military" spending towards our % too as we currently only report our actual defence budget spending towards it. Things that we don't currently include as "NATO" defence spending are our coast guard, border agency, the costs of our national policing. The portion of costs of running the plants and wages producing military munitions and equipment that we sell to others (non-NATO). The US does include many of those costs (coast guard etc).
Suffice to say, that NATO funding is not, never has been, about "
equally spending of total dollars by country"; it's about spending an equal share per citizen towards NATO. NATO (as per link above) is currently working to futher define what can/cannot be included as costs for contribuition "to NATO" spending by a nation.
% are also a very fickle thing: a high populous, yet small geographic land mass NATO nation is going to see it's % go a lot further to "defence" (Poland) than a geographicly large land mass, low population nation (Canada at 40 million population for example). Frankly Canada could spend 10% of our taxes per citizen towards the military and still not be abe to fully cover the land mass we have. NATO is looking at ways (see above link again) on how exactly to see the big pop/low land mass nations
actually be able to spend their entire allocation without doing things like ... nuking up. These anomolies are exactly why "collective defence" from attack by and for NATO nations was brought into force.
The US also has
higher military expenditures that count towards defence spending because it does project to so many parts and places in the world (not necessarily NATO nations) such as South Korea, Japan etc.
.