Final answer:
Lewis Henry Morgan's most important works include 'Systems of Consanguinity and Affinity of the Human Family', 'League of the Iroquois', and 'Ancient Society'. These works delve into the study of kinship systems, Iroquois society, and social evolution, respectively.
Step-by-step explanation:
Lewis Henry Morgan was a prominent figure in the field of anthropology. His most important work is considered to be the book titled 'Systems of Consanguinity and Affinity of the Human Family' which was published in 1871 and is housed at the Smithsonian Institution. In this work, Morgan analyzed kinship systems and family structures across different cultures.
Another significant contribution by Morgan was his research on the Iroquois people, which he documented in his book 'League of the Iroquois', published in 1851. This work is highly regarded for its examination of Iroquois political organization and social structure.
Lastly, Morgan is well-known for his pioneering studies on the evolution of human society. His book 'Ancient Society', published in 1877, introduced the concept of social evolution and provided insights into the development of human civilization.