IN Country and states drop dows ....states or not populating

Hai all i wrote this one for country and states binding in dropdown countries dropdown is working fine but states drop down is not populating

protected void BindDdlCountry()

{

SqlConnection con = new SqlConnection(s);

con.Open();

SqlCommand cmd = new SqlCommand("select * from Tb_country", con);

SqlDataAdapter da = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();

da.Fill(ds);

DdlCountry.DataSource = ds;

DdlCountry.DataTextField = "Country";

DdlCountry.DataValueField = "Id";

DdlCountry.DataBind();

DdlCountry.Items.Insert(0, new ListItem("--Select--", "0"));

DdlState.Items.Insert(0, new ListItem("--Select--", "0"));

}

___for States Dropdown__

int StateID = Convert.ToInt32(DdlCountry.SelectedIndex);

SqlConnection con = new SqlConnection(s);

con.Open();

SqlCommand cmd = new SqlCommand("select * from Tb_State where Country_Id_Pk='" + StateID + "'", con);

SqlDataAdapter da = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();

da.Fill(ds);

DdlState.DataSource = ds;

DdlState.DataTextField = "StateName";

DdlState.DataValueField = "StateId";

DdlState.DataBind();

and i never assign any of primary keys in my tables

hope someone helps me

TIA