USA was the biggest buyer and consumer of various exports from many countries. And when US consumers accumulated so much debt that they couldn't borrow and spend any more. Then they decreased their buying and consuming a lot. And that put a lot of people out of work in countries that were exporting their services and things to USA.
Also, US investment banks and officially approved rating agencies deceived a lot of domestic and foreign investors into buying mortgage backed securities. And it was a deception because the agencies that loaned the money to people for buying houses didn't care how they loaned. They didn't care if people could pay back their debts or not.
And all of this lead to large monetary losses among unsuspecting investors in USA and in many foreign countries.