If I have to answer in a sentence I would say any religion which was not born in “BHARAT” is a threat to Hinduism. The concept of not forcing your views on others is propagated by Sikhism, Buddhism, and jainism, which is related to Hinduism, whereas Abrahamic religions spread the idea that nonbelievers cannot enter heaven and should be put to death because they rebel against the one and only true god. 

The Quran and Hadiths make extremely clear in their verses that they despise kafirs.

Christianity also poses a threat to India, in addition to Islam. 

Through Christian missionaries, Christians began aiding the poor while concealing their genuine intentions. It is one of the serious threats that may soon befall India. They use the poor to convert and present the bible's partial truths. They guarantee that following conversion, they will receive housing and food. However, they refuse to display the verse Deuteronomy 13:6, which states

Educating every Muslim or Christian is not the solution because Muslims have mosques and Christians have churches where most of them go and study their holy books. They learn from maulvis and pastors why it is proper to despise non-believers and how killing them will grant you access to heaven's hoors, gardens, and divine joys. The main cause of all the honour killings is this. However, the issue is: where do Hindus go? Catholic schools. Nobody sends their children to a Gurukul because that is what backward people do; instead, modern parents enrol them in convent schools where they are taught to despise their own religion, culture, and beliefs. Other than these Abrahamic religion these Hindu converts are more dangerous.

Even though the British have left after holding us as slaves for nearly 200 years, Indians still hold the belief that they were more developed, forward-thinking, and modern. Hindus were duped by the British into believing their religion is a filthy race. 

The tolerant nature of Hindus are taken as granted. Not stating about other countries but there has been a rise in temple destruction by the supposedly peaceful people. Only during Hindu festivals do riots occur, while other religious celebrations are quiet and go off without a hitch. Vandalism of idols and stone-throwing has grown to an unprecedented degree. After watching celebrities having inter religious marriage which eventually grew popular among regular people. People never realised that these superstars white washed their faces to appear secular, but in reality, many Abduls kill their spouses or lovers if they don't accept their faith.