Here are a few causes:
* In late 80's US empire has definitely thrown international law above the board by organizing color revolutions, destabilizing other countries and waging wars
* US empire and its vassals (other NATO members) leave a trail of blood where ever they show up
* Officially, US military - despite its huge budget, infrastructure and human power - still has not (15 years later!) defeated "the terrorists"
* US empire has definitely destroyed its financial reputation in 1971 by unilaterally canceling the "gold standard" and, since then, the masks are off and US dollar is being printed/created in the computer at the speed of light, without anything but military might to back it
* World Bank and IMF - two institutions majorly influenced by the US - wreak havoc in South America, Africa, South Asia and South Europe
* Russia is getting back on feet after 2000 and US empire has no means to counter it
* US empire and its media have done something remarkable in the 26 years since the fall of the Berlin wall: In 1990 USA was a country with a great image, in 2016 USA is arguably the most hated country in the world
The world outside of the empire sees all this. And runs away from the bully who has ("long before Trump") made himself weaker by seeking refuge in those who show at least some respect.