var test = new List<Sample> {   new Sample("AT", "test1"),
                                new Sample("AT", "test2") ,
                                new Sample("AT", "test3") ,
                                new Sample("DE", "test4") ,
                                new Sample("DE", "test5") ,
                                new Sample("DE", "test6") ,
                                new Sample("AT", "test7") ,
                                new Sample("AT", "test8") ,
                                new Sample("AT", "test9")
                            };


var borderChanges = new List<Sample>();
var lastCountry = "";
foreach (var sample in test)
{
    if (sample.country != lastCountry)
    {
        lastCountry = sample.country;
        borderChanges.Add(sample);
    }
}

test.Where((x,idx) => idx == 0 || x.Country != test[idx - 1].Country));