Source: https://www.cambridge.org/core/services/aop-cambridge-core/content/view/2E38A1B9A2695DD721855BAAE690472E/S0020859016000250a.pdf/workers_politics_the_communist_challenge_and_the_schuman_plan_a_comparative_history_of_the_french_socialist_and_german_social_democratic_parties_and_the_first_treaty_for_european_integration.pdf