Complex sentence: The resolution was designed to strengthen the UN's response to complex emergencies and natural disasters, being a natural progression of the Department of Humanitarian Affairs (DHA) which replaced the Office of the United Nations Disaster Relief Coordinator (UNDRC).
Split into simpler sentences: The resolution was designed to strengthen the UN's response to complex emergencies and natural disasters. Earlier UN organizations with similar tasks had been the Department of Humanitarian Affairs (DHA), and its predecessor, the Office of the United Nations Disaster Relief Coordinator (UNDRC).