X files a patent application in France in September of 2012.
The application is published in France in February of 2014.
If X files a direct application in the United States based on the same invention, would the application in France be prior art, preventing a patent from being issued in the United States?
Different countries has different rules regarding prior applications.
Basically an invention considered not new only after the publication date, yet somtimes having a prior application would be considered double patenting.
In the US on the other hand if the publication is by the same person as in this question- the 1 year grace preiod will allow to file independently untill 2/2015.