campaign.html

<option v-for="option in country" v-bind:value="option.nicename">
{{ option.nicename }}
</option>

<script>
    export default {
        /*
         * The component's data.
         */
         data() {
            return {
                name : '',
                url : '',
                trafficsource: '',
                country: [],
                costmodel: '',
                destination: '',
                cost: '',
                redirect: '' 
            };
        },

        /**
         * Prepare the component (Vue 1.x).
         */
         ready() {
            this.prepareComponent();
        },

        /**
         * Prepare the component (Vue 2.x).
         */
         mounted() {
            this.prepareComponent();
        },

        methods: {
            /**
             * Prepare the component (Vue 2.x).
             */
             prepareComponent() {
                this.getCountries();
            },

 

            getCountries() {
                this.$http.get('/api/countries')
                .then(response => {
                    this.$set(this.$data, 'country', response.data)
                    console.log(this.$data.country);
                });
            }
        }
    }
</script>