Karl Marx explained the process of class struggle with the help of which one of the following theories ?

1. Karl Marx used the theory of dialectical materialism to explain the process of historical development, including the concept of class struggle. 2. Dialectical materialism posits that historical change arises from contradictions and conflicts (dialectic) based on the material conditions and economic relations of society (materialism). 3. Marx applied this to analyze how the struggle between different economic classes (e.g., bourgeoisie and proletariat) based on their relationship to the means of production drives historical change. 4. Empirical liberalism, Existentialism, and Darwin's theory of evolution are distinct philosophical or scientific theories and do not represent the core methodology used by Marx to explain class struggle.