As long as the war file is correctly structured and all jar files needed are in
WEB-INF/lib (except for those provided by Tomcat itself), it should work fine.
The Tomcat docs spell out what's required, as does the
Servlet Specification, or any tutorial or book on JSP/servlets.
Of particular note. Make sure that you have a
WEB-INF, which contains the web.xml. And a
WEB-INF/lib that contains the referenced jar files.
If you have any loose class files, they need to be in the package hierarchy under
WEB-INF/classes.
Do you get any errors in the logs when you start the app up? What does the manager app at /manager/html have to say?