India–Pakistan relations are the bilateral ties between the Republic of India and the Islamic Republic of Pakistan. The two countries have a complex and largely hostile relationship that is rooted in a multitude of historical and political events, most notably the partition of British India in August 1947; the India–Pakistan border is one of the most militarised international boundaries in the world. Northern India and most of modern-day Pakistan overlap with each other in terms of their common Indo-Aryan demographic, natively speaking a variety of Indo-Aryan languages (mainly Punjabi, Sindhi, and Hindi–Urdu). Two years after World War II, the United Kingdom formally dissolved British India, dividing it into two new sovereign nations: the Dominion of India and the Dominion of Pakistan. The partitioning of the former British colony resulted in the displacement of up to 15 million people, with the death toll estimated to have reached between several hundred thousand and one million people as scores of Hindus and Muslims migrated in opposite directions across the Radcliffe Line to reach India and Pakistan, respectively. In 1950, India emerged as a secular republic with a Hindu-majority population and a large Muslim minority. Shortly afterwards, in 1956, Pakistan emerged as an Islamic republic with a Muslim-majority population and a large Hindu minority; it later lost most of its Hindu population following its defeat in the Bangladesh Liberation War of 1971, which saw the secession of East Pakistan as the independent country of Bangladesh. While both countries established full diplomatic ties shortly after their formal independence, their relationship was quickly overshadowed by the mutual effects of the partition as well as by the emergence of conflicting territorial claims over various princely states, with the most significant dispute being that of Jammu and Kashmir. Since 1947, India and Pakistan have fought three major wars and one undeclared war, and have also engaged in numerous armed skirmishes and military standoffs; the Kashmir conflict has served as the catalyst for every war between the two states, with the exception of the Indo-Pakistani War of 1971, which instead occurred alongside the Bangladesh Liberation War. There have been numerous attempts to improve the relationship, notably the Shimla summit, the Agra summit, and the Lahore summit, as well as various peace and co-operation initiatives. Despite those efforts, relations between the countries have remained frigid, following repeated acts of cross-border terrorism. According to a BBC World Service poll in 2017,