Code snippet that can be used to make field country programmatically drupal 8.
$form['country'] = [
'#type' => 'select',
'#title' => $this->t('Country'),
'#options' => \Drupal::service('country_manager')->getList(),
'#wrapper_attributes' => ['class' => 'col-12'],
'#empty_value' => '',
'#required' => true,
];
