Spring MVC RESTAPI : How jackson converts list of objects to JSON format and send the response

I'm learning Spring MVC RESTAPI, Can anyone explain how the Jackson library automatically converts the list of objects to the JSON format. I can't figure out when the Jackson library comes into play and how the conversion happens from a list of objects to JSON format because I am sending the Response as a List but somehow it converts it into JSON. Can someone explain the process? Thank you.

The Jackson Library I've added :

<dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
         <version>2.4.1</version>
</dependency>

Model Class :

public class Country{

int id;
String countryName; 

public Country(int i, String countryName) {
    super();
    this.id = i;
    this.countryName = countryName;
}
public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getCountryName() {
    return countryName;
}
public void setCountryName(String countryName) {
    this.countryName = countryName;
}  }

Controller Class :

@RestController public class CountryController {

@RequestMapping(value = "/countries", method = RequestMethod.GET,headers="Accept=application/json")
public List getCountries()
{
    List listOfCountries = new ArrayList();
    listOfCountries=createCountryList();
    return listOfCountries;
}

@RequestMapping(value = "/country/{id}", method = RequestMethod.GET,headers="Accept=application/json")
public Country getCountryById(@PathVariable int id)
{
    List listOfCountries = new ArrayList();
    listOfCountries=createCountryList();

    for (Country country: listOfCountries) {
        if(country.getId()==id)
            return country;
    }

    return null;
}

// Utiliy method to create country list.
public List createCountryList()
{
    Country indiaCountry=new Country(1, "India");
    Country chinaCountry=new Country(4, "China");
    Country nepalCountry=new Country(3, "Nepal");
    Country bhutanCountry=new Country(2, "Bhutan");

    List listOfCountries = new ArrayList();
    listOfCountries.add(indiaCountry);
    listOfCountries.add(chinaCountry);
    listOfCountries.add(nepalCountry);
    listOfCountries.add(bhutanCountry);
    return listOfCountries;
}  }

When I request the getCountries() method, It just send the JSON data even though the Datatype of the method is List, How this is happening?