Complex sentence: The British believed that plainsmen generally die if they sleep in the malaria-infested zone before 1 November or after 1 June British travellers to Kathmandu went as fast as possible from the border at Raxaul in order to reach the hills before nightfall.
Split into simpler sentences: The British believed that plainsmen generally die if they sleep in the malaria-infested zone before November 1 or after June 1. British travelers to Kathmandu went as fast as possible from the border at Raxaul in order to reach the hills before nightfall.