Multiple drop down list using ajax

Below is the ajax code to perform the subjected action but it is implemented in a manner of elaboration instead of do it with simple one.

Here implemented separate code for each ajax request and response.

please see the below code:

Country :        
-select your country-     
error_reporting(E_ALL);      
ini_set('display_errors', 1);    
include "dbconfig.php";      
$result=sqlsrv_query($conn,"SELECT [CountryId],[Country] from   toilet_Country order by Country");    
while($country=sqlsrv_fetch_array($result)){      
echo "$country[Country]";      
} ?>    
 

 State :    
-select your state-     
 

 District :        
-select your District-  
 

 

Ward :       
-select your ward-    
 

     

Slum :     
-select your slum name-    
 

   

And i have written code in separate files to retrieve country,state,district information from database.
I am unaware of these ajax call request and response and looking for advise how can i make this code portable.
Thanks in advance.