using maven / manual deploy

Save your war with the name ROOT.war and deploy it, WildFly will configure it as root application.

using configuration files

In your [MAVEN_ROOT]/webapp/WEB-INF create jboss-web.xml and add:

<jboss-web>
    <context-root>/</context-root>
</jboss-web>

serve index.html

To serve your main page update web.xml:

<welcome-file-list>
    <welcome-file>index.html</welcome-file>
</welcome-file-list>