From Government and Opposition Journal April 2023 – Ludger Helms’ A State of the Field(s)

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/7D2D28956618E1FD6A0183A84D618C92/S0017257X22000252a.pdf/political_oppositions_in_democratic_and_authoritarian_regimes_a_stateofthefields_review.pdf