By a “Maven web project” I mean a Maven project which has War packaging instead of Jar (in pom.xml: <project><packaging>war</packaging></project>). When importing such projects, Eclipse may not be able to figure out that the produced War artifact may be deployed on a server.
Maven may configure your Eclipse project to support WTP:
mvn -Dwtpversion=2.0 eclipse:eclipse
This goal can also be run inside Eclipse when you right-click the project and then select: Run as -> Maven build… As goal you type in eclipse:eclipse and add a new line in the parameter table where the parameter name is wtpversion and the value is 2.0.
Running the eclipse:eclipse goal for an existing project does not affect any unrelated settings in you project.
-  Maven eclipse plugin: WTP Support