@Joker, the US is getting involved because RuSSia isn't some insignificant, little country in the middle of nowhere. RuSSia positioned itself as the rival of the US on the world stage and RuSSia's strengthening by annexing strategical lands with resources isn't something that is going to be ignored.
And I'm talking now only from the pragmatic, practical perspective, ignoring the moral and humanitarian aspect.
Let the Europeans pay for their defense its their backyard.
I bet you would be saying the same thing before the attack on Pearl Harbor if you lived during WWII.
Allowing Hitler to annex Czechoslovakia and Poland strenghtened Nazi Germany's industry and war machine making it even more powerful. By strengthening Nazi Germany the alliance of the Axis powers was strenghtened.
RuSSia isn't alone in it's appetite for "world domination". It's natural, anti-Western ally is China and other countries that are not particularly fond of the US.
So, lack of action now may have consequences in the future. Don't they teach you history in the US?
Why doesnt NATO do more to help instead of relying on the USA all the time?
What do you mean? The US is the biggest and most powerful NATO country, so it's logical that it's helping more than, let us say, Denmark. But all kinds of NATO countries are helping. Some even more than one could expect based on their size and capabilities, like the Czech Republic or Poland.