Complex sentence: The concept of an armed and mobile rural police, organised on military lines, derived from Spain's Civil Guard ("Guardia Civil"), established in 1844, which quickly won a reputation as an effective but often oppressive force.
Split into simpler sentences: The concept of an armed and mobile rural police organized on military lines, was derived from Spain's Civil Guard ("Guardia Civil"). Established in 1844 the Spanish Guardia had quickly won a reputation as an effective but often oppressive force.