European unions have their roots in revolutionary communism. They then evolved towards social democracy, which is effectively a compromise between socialism and capitalism. This social compromise, where the unions accepted market economy and private property and the employers accepted moderate unions, made the unions what they are today.

American unions evolved in another direction. Because there was no serious risk of a communist revolution, the employers had no need to comromise. Both the employers and the unions remain more confrontational than in Europe.

As a Swede who emigrated to the US:

# 1: Swedish unions are very different from US ones. They understand their companies and the country needs to be competitive on the world market. I have my problems with their power and policies, but they're vastly better for society than the US version.

# 2: The Swedish unions formed the Social Democratic party, that's been the main political power center of the country for a century. Don't know what relations they may have had with guilds in the 1800s.