If TOMCAT does not start after adding
Exception in thread "main" java.lang.UnsupportedClassVersionError: org/apache/maven/cli/MavenCli : Unsupported major.minor version 51.0
If the above error (Java execution environment is old and Maven does not work) appears in the console log, change the execution environment to Java 1.8.
Also, if you see an error such as "invalid ... header" in the "Problem" log, -Close Eclipse, delete "C: \ Users \ {each user name} \ .m2 \ repository", and restart.
Reference: [The story that the error was not solved even if the library was added using maven](The story that the error was not solved even if the library was added using maven http://hiisori.jugem.jp /? eid = 26) See also: Java 6 Unsupported major.minor version 51.0