The world economy would utterly collapse.

The crash of the US market would bankrupt many organisations that rely on US liquidity to exist.

Multinational corporations and crime syndicates and others would be at each others throats, nobody would enforce trillions worth of contracts, USD would be meaningless, all govt services would attempt to go private. mass migration attempts.

Countries with mutual treaties are going to get attacked. China would definitely take Taiwan and maybe the Philippines.

Mexiko and Canada would have a bigger coastline

The next biggest economy would likely fill the power vacuum, which at the moment would be China.
European countries would likely band together but still align their policies closer to Russian polices because they’re a more imminent threat than China.
There would probably be several small brush wars as countries try to to consolidate power amongst regional areas like North America and the Middle East.
Fragile ceasefires backed by American influence would pretty quickly dissolve like between North and South Korea.
And in a few decades everything will settle into a new “normal” just like it did when other great empires have lost their influence.

We would need to ignore how destitute the rest of the world would need to be for a superpower to full-on collapse in its entirety. I’m also assuming you mean that there’s zero semblance of order or organized society.

The military would get recalled and leave American bases, strategic territory, and other occupied areas undefended and open to capture. Economies that rely heavily on trade with the US would need to find new trading partners to prevent potential economic collapse and it might not even save them if they can’t get similar enough agreements or pricing. There are countries that also rely heavily on straight US aid, either monetarily or goods, that would collapse themselves or force them to align with whichever country would give them new aid. Global healthcare would dip without the drugs manufactured by the US. No American commodities like oil or food makes prices of those commodities go up everywhere else.

People around the world would be afraid. Whatever you may think of the American government and US politics, the average US citizen/resident is quite removed from the goings on of the federal government. The states on their own have a lot of independence and some would likely survive a collapse in federal leadership, but if federal, state, and local government all collapsed together it would be something serious enough to warrant attention from other countries with similar structure to the US.

We would probably have to learn Chinese instead of English.

Well Peace for one moment & another replacement the second moment

Don. I’ve put up with your shenanigans for months. Enough. Stop asking stupid vitriolic questions.

War

Economic chaos for a little while, and then everyone would just go on with their lives. Economically it would matter of course; America became the richest power after the first world war when all of Europe needed loans to fight their “great war”, causing the greatest transfer of wealth the world had ever seen.

But culturally, I’m betting the number of people who would give a shit if the United States stopped bossing everybody around is far less than they think it is.

The american sense of importance is strongest mostly in their own heads.

We would give a brief “Oooohh”
and then go on with our lives.

America gets a cold, the world gets the flu.

And that is just the economic impact.

dissolves for whatever reason

As if we all don’t know the reason.