Lenin’s The State and Revolution. Right into chapter one he brings up Engels’ analysis of the formation of the state:

“The state is, therefore, by no means a power forced on society from without; just as little is it ’the reality of the ethical idea’, ’the image and reality of reason’, as Hegel maintains. Rather, it is a product of society at a certain stage of development; it is the admission that this society has become entangled in an insoluble contradiction with itself, that it has split into irreconcilable antagonisms which it is powerless to dispel. But in order that these antagonisms, these classes with conflicting economic interests, might not consume themselves and society in fruitless struggle, it became necessary to have a power, seemingly standing above society, that would alleviate the conflict and keep it within the bounds of ’order’; and this power, arisen out of society but placing itself above it, and alienating itself more and more from it, is the state.”

This was extremely useful in my radicalization process, as it explained states have class characters and thus why we need a dictatorship of the proletariat.