non-module-bundler-plugin v1.0.4

  npm i --save-dev non-module-bundler-plugin

Just add the plugin to your webpack config as follows:

webpack.config.js

const path = require('path');
const NonModuleBundlerPlugin = require('non-module-bundler-plugin')

module.exports = {
  entry: 'index.js',
  output: {
    path: __dirname + '/dist',
    filename: 'index.js',
    compress: false
  },
  plugins: [
    new NonModuleBundlerPlugin({
            filename: 'libs.js',      // This is your output bundle name
            sourceFiles: [
                path.resolve(__dirname, './src/lib/script1.js'),       // paths to script files
                path.resolve(__dirname, './src/lib/script2.js'),
                path.resolve(__dirname, './src/script3.js'),
                path.resolve(__dirname, './src/lib/america_lib/script4.js'),
                path.resolve(__dirname, './src/lib/china_lib/script5.js')
            ]
        })
  ]
}

This will generate a file named libs.js in your build folder dist containing merged code of all your script files above. Set the option 'compress' to 'true' to compress and minify the result, by defaults it's 'false';