What is the main reason behind the border blockade between nepal and india?

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Due to an open border treaty between Nepal and India, citizens of both countries can move freely, work, and live across borders without passports, making tracking the movement of people difficult.Indian encroachment had long been an issue straining Nepal-India relations. Madheshis share strong socio-cultural ties to the neighbouring Indian states of Bihar and Uttar Pradesh.India had expressed concerns over the violent protests, and had asked Nepal to take Madhesi interests into consideration. The government of Nepal and the Nepalese media portrayed Madhesi movements as subversively backed by Indian infiltrators, and as an assault on their sovereignty, furthermore, Nepalis feel it is ultimately an attempt to absorb Nepal into India in whole or in part, citing the case of Nepali-dominated Sikkim.