What economic system did karl marx promote in response to the negative effects of the industrial revolution?

He promoted Socialism

Explanation:

Socialism is an economic system in which ownership of the means of production (capital such as factories, farms, banks) is common and not individual.

In socialism, the workers of factory own the factory, instead of being owned by a single person, or a few individuals who might or might not work in the factory.

Marx proposed this system because he opposed private ownership of the means of production. His main critique to capitalism is that capitalists steal part of the value workers produce. He thought that with social ownership, this exploitation would end.