And if even it is installed, it might not be in your standard library location, or might be too old of a version. From the README for XML::Parser:

This is a Perl extension interface to James Clark's XML parser, expat. It requires at least version 5.004 of perl and it requires that you have release 1.95.0 or greater of expat installed. You can download expat from:

http://sourceforge.net/projects/expat/

Of course, these sort of problems should have been caught in during the 'perl Makefile.PL' stage, as you'd have gotten a warning like:

Expat must be installed prior to building XML::Parser and I can't find it in the standard library directories. You can download expat from:

http://sourceforge.net/projects/expat/

If expat is installed, but in a non-standard directory, then use the following options to Makefile.PL:

EXPATLIBPATH=... To set the directory in which to find libexpat

EXPATINCPATH=... To set the directory in which to find expat.h

For example:

perl Makefile.PL EXPATLIBPATH=/home/me/lib EXPATINCPATH=/home/me/include

Note that if you build against a shareable library in a non-standard location you may (on some platforms) also have to set your LD_LIBRARY_PATH environment variable at run time for perl to find the library.

Of course, if you ran the make under sudo, and not the Makefile.PL, you might have different settings, which could present problems. I try to only run the 'make install' as root, and run Makefile.PL/make/make test as a non-root user. (if the program is going to be run as root, I'll sometimes also run 'make test' as root, because I've run into odd problems before, where it would pass the tests as root, or not root, but not both)