Complex sentence: Maria Luisa, who at the time had been in Spain for barely a month, had taken her father's side against the party of her brother, acted as intermediate between the deposed Charles IV and the French general Murat, who on 23 March entered Madrid.
Split into simpler sentences: Maria Luisa, who at the time had been in Spain for barely a month, took her father's side against the party of her brother. She acted as intermediate between the deposed Charles IV and the French general Murat, who on 23 March entered Madrid.