[2.0] Dropdownlist bounded to the database

[jsc0624]

I do really have the problem with this code for a couple of days now?

  protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {

            SqlConnection conn = new SqlConnection("Data Source=(local); Initial Catalog = AssetDatabase; uid = sa; pwd = oneofakinddatabase; Min Pool Size = 20;");
            DataTable dtCluster = new DataTable();
            string sqlCluster = "select * from tblCluster;";
            SqlDataAdapter daCluster = new SqlDataAdapter(sqlCluster, conn);
            int clusterID;

            daCluster.Fill(dtCluster);
            clusterList.DataSource = dtCluster;
            clusterList.DataTextField = "Cluster";
            clusterList.DataValueField = "ClusterID";
            clusterID = clusterList.DataValueField;
            this.DataBind();
        }
    }

Please examine the highlighted part? I don't really understand why it is happening that the error message says....

Cannot implicitly convert type 'string' to 'int'

I have already tried to convert this thing in asp.net using vb but the same error occurred.

Actually here is the scenario:

I have 3 dropdownlist:

1. clusterList
2. countryList
3. branchList

these three dropdownlists are bounded in the database (sql server database).
First thing first, I am going to choose one from the clusterList.
ex.
clusterList contains the ff:

ASIA
EUROPE
AMERICA

of course those cluster have their own ID assign let say:
ID CLUSTER
1 ASIA
2 EUROPE
3 AMERICA

That's why from my code I tried to assign the ClusterID to DataValueField hoping that it would be recognized by the program, in order for me to use that ID for the WHERE CLAUSE of the sql statement for the countryList:

            daCluster.Fill(dtCluster);
            clusterList.DataSource = dtCluster;
            clusterList.DataTextField = "Cluster";
clusterList.DataValueField = "ClusterID";

The said ClusterID will be available for the next sql statement:

clusterID = clusterList.DataValueField;

lets say here is the second sql statement for the countryID:

string sqlCluster = "select * from tblCountry where clusterID = " + clusterID +";"

so to make the story short:

DropDownList1 will present ASIA
DropDownList2 will present all the countries in ASIA

and if I am going to choose Malaysia for example, the DropDownlist3 will presents all the store branches that can be only found in Malaysia.

I hope you understand what I mean even I am poor in English. Thank you in advance.