As His Holiness the Dalai Lama explained (in a teaching in Finland, 1988):

"What is common to all the four major traditions of Tibetan Buddhism is their emphasis on the practice of the entire structure of the Buddhist path, which comprises the essence of not only the Vajrayana teachings, but also the Mahayana practices of the bodhisattvas, and the basic practices of the Fundamental Vehicle".

The Buddhism practiced in Tibet is unique in that it includes the Vajrayana path as a natural conclusion whereas in other national traditions the Vajrayana isn't necessarily included in the practice of the Mahayana.