What got fixed in the 20th century? Humankind was brought to the brink of annihilation through nuclear weapons, the world got poisoned with PFOA, global warming accellorated, the American empire became the most dangerous empire ever, obesity and diabetes became epidemics and young people got robbed of their future. The human species isn't the problem, it's less than 0.1% of the species causing 99.9% of the problems.