Bhutan is a South Asian country in the Eastern Himalayas and is bordered by Tibet and India. The independence of Bhutan has endured for centuries and it has never been colonized in its history. Situated on the ancient Silk Road between Tibet, the Indian subcontinent and Southeast Asia, the Bhutanese state developed a distinct national identity based on Buddhism. In the 19th century, the House of Wangchuck united the country and in 2008 Bhutan transitioned from an absolute monarchy to a constitutional monarchy. The country's landscape ranges from lush subtropical plains in the south to the sub-alpine Himalayan mountains in the north, where there are peaks in excess of 7,000 meters (23,000 ft). Bhutan is perhaps most notable for pioneering the concept of gross national happiness.