Maven dependencies automatically removed from web deployment build in eclipse

Question

I started a web application project in eclipse, added the nature of maven to simplify loading and dependency management, and created some files.

Each time I add a new dependency to my pom.xml (to use a specific class A) and then update the project, tomcat says that it cannot load class A (although it is included in the build path and exists on the file system). To solve this problem, I add "Maven dependencies" to the project deployment assembly.

The problem is that I need to re-add "Maven dependecies" to the project deployment assembly every time I add a new dependency ... because it just gets removed, possibly when tomcat stops or redistributes.

Could you explain to me why maven dependencies are not automatically included in a project that has the character maven, and especially why "Maven dependecies" are removed ..

thank