Complex sentence: The Palmyrene Empire (270--273), was an Aramean kingdom it was a splinter state centered at Palmyra, that broke away from the Roman Empire during the Crisis of the Third Century.
Split into simpler sentences: The Palmyrene Empire (270--273), was an Aramean kingdom. It was a splinter state centered at Palmyra that broke away from the Roman Empire during the Crisis of the Third Century.