auto_create_campaigns()

add_action( 'set_object_terms', 'auto_create_campaigns', 10, 6 );
function auto_create_campaigns( $object_id, $terms, $tt_ids, $taxonomy, $append, $old_tt_ids ) {
    if ( 'campaigns' !== get_post_type( $object_id ) || 'country' !== $taxonomy ) {
        return;
    }

    if ( $append ) {
        $term_ids = $tt_ids;
    } else {
        $term_ids = array_diff( $tt_ids, $old_tt_ids );
    }

    $post = get_post( $object_id, ARRAY_A );
    unset( $post['ID'] );

    foreach ( $term_ids as $term_id ) {
        $term = get_term( $term_id, $taxonomy );
        if ( is_wp_error( $term ) || empty( $term ) ) {
            continue;
        }

        $post['post_title'] = $term->name;
        $post['post_name'] = $term->slug;
        $post['post_parent'] = $object_id;

        $post_id = wp_insert_post( $post );
        error_log( sprintf( 'Post%s created.%s',
            $post_id ? '' : ' not',
            $post_id ? ' ID: ' . $post_id : ''
        ) );

        // Set post terms.
        remove_action( 'set_object_terms', 'auto_create_campaigns', 10, 6 );
        /*if ( $post_id ) {
            // Copy the parent's "countries".
            // wp_set_post_terms( $post_id, $terms, $taxonomy );
        }*/
        add_action( 'set_object_terms', 'auto_create_campaigns', 10, 6 );

        /*if ( $post_id ) {
            // Copy the parent's custom fields.
        }*/
    }
}