Webpack not running from the root directory

For some reason, when I try to run webpack from the root directory, I get a "throw err; Error : Cannot find module 'webpack'" even though I installed it globally. It works if I go into the app directory.

My todo.bundle.js file still looks like it did in the video before adding all the angular dependencies, even though I went back and added everything.

Here's my code, just in case -

app.js:

'use strict';

var angular = require('angular');

angular.module('todoListApp', []);

require('./scripts/controllers/main.js');
require('./scripts/controllers/todo.js');
require('./scripts/directives/todo.js');
require('./scripts/services/data.js');

main.js (sample...all of the required files have the require angular line added):

'use strict';

var angular = require('angular');

angular.module('todoListApp')
.controller('mainCtrl', function($scope, dataService){

  dataService.getTodos(function(response){
    var todos = response.data.todos;
    $scope.todos =  todos;
    });

  $scope.addTodo = function() {
    $scope.todos.unshift({name: "This is a new todo.",
                      completed: false});
  };

})

What did I do wrong? I'm not sure if not being able to run webpack outside of the app folder has something to do with it, but it may be something else entirely. Thanks.