> Europe will lose some territory but gain it's own military security after decades of living from the US strategy alignment.
Why would that be the outcome? Why wouldn't it result in European countries wanting more US involvement? Who wouldn't want the most powerful country in the world on their side, as their ally?
Also, I strongly disagree with the idea that separately, the US and Europe are somehow stronger. Separately, countries end up in conflict - Europe's own history shows it especially, and that's one of the primary, intentional reasons for NATO and the EU. Together they are far more powerful - NATO is far more powerful than any country alone, including the US.
The EU - which for all its flaws is, if you step back and look from an historical perspective, arguably the greatest international organization in history - still lacks effective, unified international relations. Decisions require unanimity, which is hard for a small organization, and now they have dozens of members. Kissinger famously said (iirc), 'if I have to call Europe, who do I call?' They don't yet have the political structure and institutions to conduct international relations as whole.
Finally, power in international relations ultimately flows from wealth and population. If China continues to grow, it could have an economy twice the size of the EU's (or US's) within decades, and India has potential for similar growth. Together, the US and EU offer a much stronger balance.