mvn archetype:generate -DartifactId=my-webapp -DarchetypeArtifactId=maven-archetype-webapp

Note the packaging element - this tells Maven to build as a WAR. Change into the webapp project's directory and try:

mvn clean package

You'll see target/my-webapp.war is built, and that all the normal steps were executed.

Now you can modify this webapp project and turn it into anything you need!