War is fundamentally different now than it was at the beginning of WW2. A nuclear superpower cannot be invaded. You can poke the bear A LOT, but basically everyone recognizes that a ground invasion is crossing a red line.

That's the purpose of NATO. In exchange for giving up some autonomy to the US (letting the USA build military bases in your territory, not acting overtly against our interests), and paying us for our fancy weapons, NATO members get the immeasurably valuable power of a nuclear red line border, and protection by the most powerful military the world has ever seen. It's a very, very good deal, and the most stabilizing force in history.

Given the NATO membership of most of Europe, the only wars possible in Europe are small, regional conflicts between non-member states.