Japan made better cars in the late 60s and 70s and put the hurt on Detroit.
Detroit was making lousy cars compared to the Japanese and it finally caught up to them.
Tariffs kept the Japs out for awhile but they built plants in the States to get around them.
Once it became a even competition the Big 3 got their butts kicked.
Also was the rise of the unions (UAW) which increased labor costs greatly and basically killed the jobs.
You had the Big 3 sourcing parts from cheaper foreign countries and building plants outside the U.S.
Cheaper foreign labor, less regulations, lower taxes and there goes Detroit.
80% or so of a Ford truck is foreign made parts now.