How do I fix a runtime error when using webpack with React?

Question

How would I even start to debug this issue with my webpack failure to compile file in my terminal?

Here is the error in the terminal:

ERROR in ./app/components/App.js
Module not found: Error: Can't resolve 'react-router-dom' in '/Users/andrewtalle/Desktop/github-battle/app/components'
 @ ./app/components/App.js 21:18-45
 @ ./app/index.js
 @ multi (webpack)-dev-server/client?http://localhost:8080 ./app/index.js

ERROR in ./app/components/Home.js
Module not found: Error: Can't resolve 'react-router-dom' in '/Users/andrewtalle/Desktop/github-battle/app/components'
 @ ./app/components/Home.js 21:11-38
 @ ./app/components/App.js
 @ ./app/index.js
 @ multi (webpack)-dev-server/client?http://localhost:8080 ./app/index.js

ERROR in ./app/components/Nav.js
Module not found: Error: Can't resolve 'react-router-dom' in '/Users/andrewtalle/Desktop/github-battle/app/components'
 @ ./app/components/Nav.js 3:14-41
 @ ./app/components/App.js
 @ ./app/index.js
 @ multi (webpack)-dev-server/client?http://localhost:8080 ./app/index.js
Child html-webpack-plugin for "index.html":
     1 asset
    Entrypoint undefined = index.html
    [./node_modules/html-webpack-plugin/lib/loader.js!./app/index.html] 324 bytes {0} [built]
    [./node_modules/lodash/lodash.js] 527 KiB {0} [built]
    [./node_modules/webpack/buildin/global.js] (webpack)/buildin/global.js 492 bytes {0} [built]
    [./node_modules/webpack/buildin/module.js] (webpack)/buildin/module.js 546 bytes {0} [built]
ℹ ｢wdm｣: Failed to compile.