A number of reasons could explain why the US was not in phase with the EU (Germany) on this one in the 1980s and 90s
> because Germany was charting its own course at the time without prior US "approval"
> because of disagreements about the new perimeters of influence in the region (namely between US and Germany)
> because of disagreement about who would get which ex Yugoslav asset (mines, industry, real estate)

... culminated in public maneuvering which exposed rifts between the US and its European (German) ally.