add list using
<asp:ListItem Value="United States" Text="Canada"></asp:ListItem>
and then try
DropDownList1.SelectedItem.Text
I found your mistake.
<asp:ListItem>United States</asp:ListItem>
change this to
<asp:ListItem>United States1</asp:ListItem>
Then you will got the actual value.
What was the issue is, there are two same values in your dropdown, when page postback, it take first value as selected and give the result accordingly. if you noticed when after postback United State Value is selected