Why did Karl Marx say capitalism was doomed?

Karl Marx argued that capitalism was doomed due to its inherent contradictions, particularly the conflict between the bourgeoisie (capital owners) and the proletariat (workers). He believed that capitalism would lead to increasing inequality, exploitation, and alienation, ultimately resulting in class struggle. This struggle would culminate in a proletarian revolution, overthrowing capitalism and establishing a classless society. Thus, Marx viewed capitalism as unsustainable in the long term, destined to be replaced by socialism and communism.