I think that people all around the world grow up with the mindset that America is one of the freest and best places to live, especially in third world countries or ones not ruled by a democracy. Many of the same countries and others hold faith that the US stands as a barrier or last bastion against global terrorism, dictators taking over, Russia, China, etc as they are one of the strongest nations on the planet. America doesn't hold protests like this very often, if ever reaching this level of hysteria. People around the world see that and are concerned that if the supposed best country in the world is on the brink of fascism or "collapse", what dominos will fall after they do. Therefore, they start protesting in their own countries in solidarity with the United States, hoping to ensure that the correct change happens in America, keeping the preferred global power in a democracy and not a fascist country like many others that they are afraid of.

I feel like I jumped around a lot in this but the main concept is if America falls from its perch above or with other top countries or changes from the free democratic country that it is, the domino effect this will have on smaller countries and the world in general will be huge, and that's why other countries are protesting.