Why do many people conflate post-Marxism and post-modernism?
The two are actually rather different and in some ways even opposing schools of thought. For example, while post-Marxists would look at the (real or perceived) historical imbalances in power and wealth between Wales and England, and what has formed the relationship between the two nations, post-modernists would say "what is Wales and what is England?", arguing that they (and nations in general) are merely "social constructs" that ultimately mean whatever people want them to mean.