http-request.js

 created() {
    // Making the http request with Fetch API
    const API = 'https://restcountries.eu/rest/v2/all';
    
    fetch(API, {method: 'GET'})
    .then(res => res.json())
    .then((json) => {
      // Place results into the state property
      this.countries = json;
    })
    .catch(err => console.log(err));   
  },

rendering-countries.html

<ul>
    <li v-for="country in countries" :key="country.id">
      {{ country.name }}
    </li>
</ul>