Complex sentence: In 1875 Kristiania Sporveisselskab (KSS) started the first horsecar services in Oslo--at the time called Kristiania--followed by Kristiania Elektriske Sporvei (KES) who established electric tram services in 1894; by 1900 KSS had also converted its routes to electric traction.
Split into simpler sentences: In 1875 Kristiania Sporveisselskab (KSS) started the first horsecar services in Oslo--at the time called Kristiania. It was followed by Kristiania Elektriske Sporvei (KES) who established electric tram services in 1894; by 1900 KSS had also converted its routes to electric traction.