Many of those deaths were caused by famine, which one could argue was caused by Mao's policies, but I dunno.
China is a big country no famine in the 20th century could have caused 80million people to die. People don't realize this but china is actually great for agriculture and historically has always been so. It's why China has even in ancient times had a huge population, the land there is very fertile. In fact this is probably the least amount of Chinese people on earth in thousands of years from a proportion of total population perspective, largely due to the communists restricting families to one child each. The number 1 determinant of population growth is agricultural efficiency.
There is no way 80 million people dying in a place with such established agricultural practices was from natural causes. Mao wanted to institute his great leap forward which caused it