I'd say the 70s is when a lot of problems came in. That marked the legalization of abortion, the beginning of the gay rights movement, fomenting of evolutionary psychology, and the creation of no-fault divorce.
However, economically it also marked the beginning of free trade agreements like NAFTA that would spell the destruction of our manufacturing industry and a new period of warmongering per Vietnam. Shortly afterwards, CEO compensation skyrocketed from 35 times the pay of the average work in 1978 to 300 times by 2000. Deregulation resulted in the growth of fascism, i.e. corporate rather than democratic control, and a resurgence of the monopolization that Teddy Roosevelt and his era of trustbusting in the early 1900s had stamped out.
Because of American intrusion in Vietnam and elsewhere, we began to destroy the worldwide goodwill we had built up following WWII, even as we let China parasite our economy by using a much lower minimum wage to take all of the economic growth with its cheap workforce, destroying the economic strength that made us the predominant world power.