The treaty that established the boundary line of Nepal, was signed (Parish Bradshaw for the Company & Guru Gajaraj Mishra for Nepal) on 2nd  December, 1815 and ratified by 4th March, 1816 between the East India Company and King of Nepal following the Anglo-Nepalese War of 1814-16 is called as The Treaty of Sugauli (also spelled Sugowlee).
The war ended with the signing of the Treaty of Sugauli in 1816, which surrender around one-third of Nepal's territory to the British. Furthermore, according to the treaty, Nepal had to allow for the establishment of a permanent British resident in Kathmandu and had to forgo all self-determination in foreign affairs. The political map during that time was like as posted.

But when there was another treaty signed, the official name for The Treaty of Peace and Friendship between the Government of India and Government of Nepal , was  a bilateral treaty between two neighbours countries establishing a close strategic relationship. The treaty was signed at Kathmandu on 31st July, 1950 by the last Rana Prime Minister of Nepal Mohan Shumsher Jang Bahadur Rana and Indian ambassador to Nepal, Chadreshwar Narayan Singh and came into force the same day as per Article 9 of the Treaty. After the short interval of time of the treaty signed about 3 months passed The Rana rule in Nepal was ended. The treaty allows free movement of people and goods between the two nations and a close relationship and collaboration on matters of defense and foreign policy.

Why did British India Company not invade Nepal ?

The British were just in the process of consolidating their power in South Asia. So that, East India Company had made decision not to associate the main  Nepalese territories because annexation of Nepal would had unwittingly brought them in close confrontation with the Qing Empire, which they tried to avoid at all cost.
Facts about Nepal-India Borders Disputes?

As we know that Nepal is surrounded by India in the three sides and Northern part by The Republic of China.  Due to the open and unregulated border system, the border problem is increasing day by day in comparison to other side but there can be issues if we go through. We can see more encroachment to the south side after The Sugauli treaty, it started to increase gradually. In fact after the independence of India in 1947 AD, India started to increase border territory disputes. The origin place of Mechi River, Antu Hill Region, The region of Ramnagar, Northern of Chure mountain to southern side, jungle etc. are regarded as the disputed border areas. The encroachment dispute increased in 10 yards (Dashgaja) region due to population increase in India, due to deforestation of Nepal’s four-sided jungle or bush by Indian, and due to encroachment of Nepal’s land. Susta, Arra, Nala, Tal Bagonda etc. are the disputed   border areas where even border pillars are not found.



When the democracy was established in 2007 BS in Nepal, then the encroachment started to increase in the area of Kalapani-Limpiyadhura and Susta as well as the Indian people increased encroachment by deforesting the Nepalese jungle. Even after the re-establishment of democracy in 2046 BS, the land encroachment continued in the places such as Tanakpur, Mahespur, Thori, Susta, Sandakapur, Manebhanjyang, Pashupatinagar, Bhantabari,  the Mechi Pul area (two third) of Kankadvhitta. Indian built dam and embankment in different places such as Laxmanpur, Rasiyawall- Khurlotan, Mahalisagar, Kohalawas, Kunauli. Moreover, after the political change in 2062/063 BS, the encroachment did not stop, yet, it has been encroaching in the places such as Lalbojhi and Bhajani in Kailali, Chaugurji of Gulariya in Bardiya, ParasanParatal in Kanchanpur, 1.5 km of Koshi embankment towards east-west highway and the encroachment of Susta is even increasing.
Of the 26 districts of Nepal sharing border with India, 21 districts, in 54 places, are facing the problem of violation of their territory by India.  It is estimated that more than 60,000 h. land of Nepal has been encroached by Indian side. Of this, the most disputed area is Kalapani-Limpiyadhura where the largest chunk of land (37,000h.) has been encroached. Similarly, the land of Nepal has been encroached in different places in different chunks such as Susta (14,000h.) the region of the Mechi river bank (1,600h.), while constructing Sarada barrage (8.85h.), Sandakpur (2h.), Parasan Pyara Tal (450h.), Bhajani Lalbojhi (330h.) Korobari (40h.), Gulariya (6h.), Guphatal Manebhanjyang (4h.), Jhitkaiya (3h.) and Pashupatinagar (240 sq km) is the least chunk of land encroached area. The most heated disputed area is Kalapani where  372 sq. km towards Limpiyadhura from Kalapani has been encroached by Indian Army.

The Sugauli treaty has specified that the Kali River as the border of the two countries. Still there is dispute about the origin of the Kali River where we can find three places Limpiyadhura, Lipulek and Kali temple which one is the origin place of Kali River has not been specified yet. The old maps and records show Limpiyadhura is the origin place of the Kali River. It is the largest chunk of land that has been encroached by India.  Although claimed by Nepal, Kalapani is currently being occupied by India's security forces since the 1962 border war with China.India is saying that except Susta and Kalapani, there is no dispute regarding border line between Nepal and India.  

NEGOTIATION
Where there is ray, there must be way so to solve the Border Problem and  disputes between the two countries should be solved by dialogue in couteous way and reverentially. If the dialogue needs to be on diplomatic and mediator settlement, we should ask for help of the United Nation Organization.Yet, if the problem could not solve, then mutual understanding to go for international court is only one way because due to the circumstances of The Treaty of Sugauli, one side cannot claim their border issues on subject to make it as International Justice.

CONCLUSION
If encroachment continues at the current rate and if we continue to watch silently, millions of people will soon become aliens and our nation and nationality will be under serious threat. Eventually, it could even end of Nepal’s existence in the near future. Hence, the border issue should be solved as soon as possible.
Thanks for the Nepalese Government for issuing the new political and administrative map which was actual, is actual and will be actual.