You can do this:
If your tomcat installation is default and you have not done any changes, then the default war will be ROOT.war. Thus whenever you will call http://yourserver.example.com/, it will call the index.html or index.jsp of your default WAR file. Make the following changes in your webapp/ROOT folder for redirecting requests to http://yourserver.example.com/somewhere/else:
Open webapp/ROOT/WEB-INF/web.xml,
remove any servlet mapping with path /index.html or /index.jsp,
and save.
Remove webapp/ROOT/index.html, if it exists.
Create the file webapp/ROOT/index.jsp with this line of content:
<% response.sendRedirect("/some/where"); %>
or if you want to direct to a different server,
<% response.sendRedirect("http://otherserver.example.com/some/where"); %>
That's it.