I've created a Maven project, of packaging type "jar", called "Y"
I've done "Maven install", and I could find it in my local repository..
Then, I've created another project, of packaging type "war", called "X". In this project, I added a dependency to "Y" jar, as follows :
Project 'X' is missing required Java project: 'Y'
Thank you @Eldad, your comment helped me to detect the problem.
Under Eclipse IDE : Right click on "X" project > Build Path > Configure Build Path > Project > Check Y > Click on "Remove"
Now no error while deploying the X war.