Combobox static item in xaml seleted item in MVVM in Silverlight

<usercontrol x:class="ComboxApp.SearchUC" xmlns:x="#unknown">
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:sdk="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400"&gt;
    
    <grid x:name="LayoutRoot" removed="White">
        <combobox x:name="CBCountry" grid.column="0" height="23" grid.row="0" width="130" selecteditem="{Binding Country,Mode=TwoWay}">
            <comboboxitem tag="US" content="US" />
            <comboboxitem tag="CA" content="CA" />
        </combobox>
    </grid>
</usercontrol>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using ComboxApp;
namespace ComboxApp
{
    public partial class SearchUC : UserControl
    {
        public SearchUC()
        {
            InitializeComponent();
            MainPageViewModel mvm = new MainPageViewModel();
            this.DataContext = mvm;
        }
    }
}

<usercontrol x:class="ComboxApp.MainPage" xmlns:x="#unknown">
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:local="clr-namespace:ComboxApp"
    mc:Ignorable="d"
    d:DesignHeight="300" d:DesignWidth="400" 
    xmlns:my="clr-namespace:ComboxApp"&gt;
    <usercontrol.resources>
        <local:mainpageviewmodel x:key="myviewmodel" xmlns:local="#unknown" />
    </usercontrol.resources>
    <grid x:name="LayoutRoot" removed="White">
        <local:searchuc x:name="ucCustomerSearch" grid.row="0" datacontext="{Binding Source={StaticResource myviewmodel}}" xmlns:local="#unknown" />               &lt;Button Content="Button" 
                Height="23" 
                HorizontalAlignment="Left" 
                Margin="123,188,0,0" Name="button1" 
                VerticalAlignment="Top" 
                Width="75" Command="{Binding Source={StaticResource myviewmodel},Path=GetSelect}" /&gt;
        
    </grid>
</usercontrol>

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.ComponentModel;
namespace ComboxApp
{
    public class MainPageViewModel : INotifyPropertyChanged
    {
        public MainPageViewModel()
        {
            SelectedItem = new Country();
            SelectedItem.Text = "US";
            GetSelect = new CommandBase(GetSelectedItem);
        }
        
        private Country _selectedItem;
        public Country SelectedItem
        {
            get { return _selectedItem; }
            set { _selectedItem = value; 
            NotifyPropertyChanged("SelectedItem"); }
        }
        public ICommand GetSelect
        {
            get;
            private set;
        }
        private void GetSelectedItem(object parameter)
        {
        }
        
        #region INotifyPropertyChanged Members
        /// <summary>
        /// Notifies when properties are changed  
        /// </summary>
        public event PropertyChangedEventHandler PropertyChanged;
        private void NotifyPropertyChanged(String info)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(info));
            }
        }

        #endregion
    }
}