Well, it's always to blame others .. Our sectarian problems and strife is very much homegrown
Our very own Sheikh Ahmed Sirhindi, revered as Mujaddid Alif Sani (the reviver of the second millennium) was issuing Fatwas declaring it obligatory for the Sunni rulers and common men to kill Shias (whom he declared worst kafirs) and confiscate their properties and belongings, as early as the 16th century. Although initially imprisoned by the Mughal Emperor Jahangir, he was subsequently made a part of the Mughal Royal Camp. He greatly utilised this position of power and in a few years became the most prominent and influential scholar of India. Around the same time, a struggle was going on in the Pashtun belt between the followers of unorthodox Pir-e-Roshan followers and orthodox Pir Baba and Akhund Darweza (buried in Peshawar) followers. Mughal emperors had declared war on the followers of Pir-e-Roshan which ultimately led to emergence of Akhund Darweza's orthodox Islam as the prominent version/interpretation of Islam in the Pakhtun areas, something that has remained unchanged ever since.
Then, in the 18 century, came another very famous and influential scholar Shah Waliullah Dehalvi, another fiercely Anti-Shia preacher, who besides issuing decrees banning Shia religious practices, strongly advocated that the Arab way was the right way. Shah Waliullah and Abdul Wahhab Najadi were both students of Muhammad Hayyat ibn Ibrahim al-Sindhi, a Naqshbandi follower of Ahmed Sirhindi from Sindh (present day Pakistan) and a staunch admirer of Ibn e Taimiyyah. Ahmad Shah Abdali was persuaded by Shah Waliullah to invade India and kill/expel Marathas as well as Shias from Delhi. No Shia remained in Delhi after Abdali's invasion.
Maulana Abul Kalam Azad, Allama Mohammad Iqbal, Abul A’la Maududi and many others carried forward the tradition of Waliullah with slight re-adjustment. And then came his son Shah Abdul Aziz, the man who shaped the Sunni attitude towards Shia and vice versa (in the form it exists today) through his writings. Deoband was just a continuation of the exclusivist and sectarian legacy of Sheikh Ahmed Sirhindi, Shaha Waliullah, Ahmed Shah Abdali and others.
We can go on and on. Our sectarian problem is not imported, it's very much homegrown and has deep roots in our history. Factors like Saudi/Iranian funding only exploit the already existing fault lines
