Differences between the European Union and the United States have raised questions about the defence of Europe - should it be based on Nato or in the long run should it defend itself?
The US fears the plans will undermine Nato's influence
There are some who see in this the first fractures in the defence relationship between the United States and Europe, the inevitable result of the removal of the threat from the Soviet Union.
Others hope that an agreement can be reached which smoothes over the problem and allows a harmonious role both for Nato and the EU.
Defence and the EU
The issue has arisen because the draft EU constitution envisages moves towards a more active role for the European Union in defence.
It states that there should be "the progressive framing of a common Union defence policy.
"This will lead to a common defence, when the European Council, acting unanimously, so decides."
Meanwhile, the treaty adds, the EU should undertake "peacekeeping, conflict prevention" and other missions. It does so already on a limited scale.
But references to peacekeeping and other operations leads right to the point of how they should be organised. This is where philosophical differences lead to practical problems.
US and French differences
The United States is happy enough for the EU to do what Nato does not want to do. But it insists that there should be no overlapping and no rivalry.
The French on the other hand appear to see an opportunity to develop purely European structures.
They proposed, with German and Belgian support, to set up an EU military headquarters in the town of Tervuren to the west of Brussels.
That plan has now been put aside as part of the negotiations, but the thinking was clear - the EU needs some kind of separate defence identity.
France has a history of distancing itself from Nato while remaining a member. General de Gaulle threw Nato out of its headquarters there and France later withdrew from Nato's integrated military structures.
Britain in the middle
In the middle, as usual, have been the British, nervous about undermining the American commitment to Europe and yet mindful that in future that commitment may diminish.
A compromise has been proposed by Britain, France and Germany. Under this, and it still has to be finally accepted by all parties, any EU planning unit or units will work closely with Nato and not against it.
To help sweeten the pill for Atlanticists, Britain has suggested putting an extra line in the EU constitution about Nato being the "foundation" of collective defence for Nato members.
The German Foreign Minister Joschka Fischer said: "All we want is complementarity not competition."
It might be thought that planning units are small and insignificant. But they have a habit of growing.