Complex sentence: Since then, tourism in Nepal has blossomed and as a result it is sometimes said to be the "third religion" of Nepal, as the country's most important industry that plays a large role in the economic activity of Kathmandu.
Split into simpler sentences: Since then, tourism in Nepal has blossomed; as a result it is sometimes called the "third religion" of Nepal. It is the country's most important industry that plays a large role in the economic activity of Kathmandu.