Should work just about as well as the EU.
The last time they had a “European army” they invaded the
Soviet Union; they failed because we propped up Stalin...
and the Germans will end up in charge, just like the EU, the Brits will threaten to leave, the French will underperform to the point of where they just want to be involved (at first, then later in charge of— after the Germans take over the firepower) noncombatant operations.
The only way I see this going forward is a suitably agreeable means for all involved to do economic stimulus on a continent-wide scale...we can’t rely on America anymore, we have no fighting force of our own...we’ll have to build the weapons platforms and train the personnel...
Guns and butter.