Custom Widget function in Plugin not working?

I took a code straight out of one of my themes I created, and it’s a list of all 50 states in an unordered list packed into a widget you can just drag and drop on the sidebar.

The problem is, when I try using this code in a PLUGIN file, I get the following error:

Fatal error: Call to a member function register() on a non-object in C:\xampp\htdocs\wordpress\wp-includes\widgets.php on line 431

Why would it work in the theme, but not in the plugin? By the way, the active theme is NOT the theme I took the code out of.

Here’s my code: http://pastebin.com/ZeRWW3yb

Thanks.

try replacing :

register_widget('States_Widget');

with:

add_action('widgets_init', 'register_states_widget');
function register_states_widget() {
    register_widget('States_Widget');
}