During the early period the invaders exploited the internal strife of the petty hill chiefs and started subjugating them one by one.
They integrated the adjoining feudatories to form larger kingdoms as far as possible. During the period 629 A.D. to 644 A.D., several foreign invaders
invaded some parts of Himachal Pradesh. The Kir tribe of Yarkand invaded the kingdom of Chamba killing the ruler Luxmi Verman. Similarly Tibet invaded Lahaul-Spiti in which it was helped by the king of Kullu. In this period the administration was also of the primitive type. The lack of king’s personal interest in the state work offered opportunities to Thakurs and Ranas to declare themselves independent. This was also a golden period of culture and civilization. Since the kings and their subjects had a deep faith in religion, many temples were built in different parts of Himachal Pradesh. During this very period Padam Sambhava propagated Buddhism in Tibet. Buddhism also spread in areas of Kinnaur and Lahaul-Spiti during this period.
During medieval period, the older, larger states of Kullu, Kangra, Mandi, etc., were broken and many new small states came into being. The small states of Guler,
Siba, Datarpur, Handur, Koti, Bhaggi, Kumarsain, Khaneti, etc., came into existence. During this period Muslims, Mughals, British, Dutch, Portugese and French invaded many parts of India.
The relations between Mughals and these hill states started with Akbar who sent Todar Mal to annex Kangra and ruler of Kangra, Dharam Chand accepted his sovereignty. Later in 1620 A.D., during the reign of Jehangir, Kangra came under Mughal rule which continued for a long time. During the reign of Aurangzeb, when the foundations of the Mughal rule started rocking under the pressure of Marathas Guru Gobind Singh, the tenth Guru of Sikhs, made efforts to unite these warring hill states and fortify the strategic location of these hills with persuasion and force. The Mughal never intervened in the internal matters of these hill rulers who continued warring among themselves as usual. The victorious rulers used to dictate terms to the defeated ones. After the death of Aurganzeb, the Mughal rule in India was on the decline. At this juncture, Gurkhas, Sikhs and Marathas were emerging as strong powers on the political horizon of India. The Gurkhas conquered almost the whole of the western Himalayas by 1805 A. D.
However, people soon got tired of the harsh and tyrannical rule of the Gurkhas. They united themselves and took a stand against them. Raja Sansar Chand fought severely with the Gurkhas from inside the Kangra fort for about four years, during which the economy of Kangra was badly shattered. He requested Maharaja Ranjit Singh for help. After getting hold of the Kangra fort, Maharaja Ranjit Singh proceeded to conquer other hill states and annexed many of the Himachal principalities. In 1842 A. D., with the annexation of Ladakh by the Sikh General Zorawar Singh, the territory of Lahaul-Spiti became a Sikh possession. After the Anglo-Sikh war of 1845 A. D., the British took over the territories of Lahaul-Spiti and Raja Gulab Singh was recognized as an independent ruler, both by the Sikhs and the British. The entire hilly area lying between the Satluj & Yamuna Rivers with the exception of Kullu and Mandi was awarded to him for his services rendered to the British during the Anglo-Sikh war. In 1848 A. D., all the ruler of this area, tried to liberate their territories with the help of Sikhs, but were defeated and the rebel rulers were killed. This caused great resentment among the chiefs. In 1857 A. D., they revolted along with some other princes. By the mid-nineteenth century, parts of Kangra, Kullu, Lahaul, Spiti, Kotgarh, Kothaki etc., had come directly under the British Empire.
When India became independent, the native Indian states remained under the yoke of feudalism, in spite of appeal of national leaders for the merger of Punjab states and Punjab hill states. On January 26’1948, decision was taken by the All India State People’s Conference urging the national leadership to merge all hill states to form one state. In order to carry out a greater Himachal, on November 1’ 1966, Kangra, Kulu, Lahaul and Spiti and Shimla district of Punjab were integrated with it. Full statehood was granted to Himachal Pradesh on January 25’1971 with Shimla as its capital.